Here you go. I didn't bother testing this through the mount because it already failed directly via rclone to remote. So hmm... not sure how to make this fit with the other observations. Very strange that you had no problems on the same setup - unless it really is a wrong persmissions setting somewhere.
TLDR of log: same insufficient permissions error when setting modtime. This was done against an existing file (one of those that had gotten it's mod-time not updated).
C:\rclone>rclone touch -vv --dump bodies -t 1001-01-01T00:00:00 "Gcloudtest:rclonestore\SMALLFILE (31).txt"
2019/08/23 21:07:31 DEBUG : rclone: Version "v1.48.0-227-g077b4532-beta" starting with parameters ["rclone" "touch" "-vv" "--dump" "bodies" "-t" "1001-01-01T00:00:00" "Gcloudtest:rclonestore\SMALLFILE (31).txt"]
2019/08/23 21:07:31 DEBUG : Using config file from "C:\rclone\rclone.conf"
2019/08/23 21:07:31 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2019/08/23 21:07:31 DEBUG : HTTP REQUEST (req 0xc0000f0b00)
2019/08/23 21:07:31 DEBUG : POST /token HTTP/1.1
Host: oauth2.googleapis.com
User-Agent: rclone/v1.48.0-227-g077b4532-beta
Content-Length: 789
Content-Type: application/x-www-form-urlencoded
Accept-Encoding: gzip
assertion=eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6IjRjMTNmMzUyZmQ5N2YxN2ZmMmY3NmYwNTk3NzYzMzcyY2I2MzBhOWIifQ.eyJpc3MiOiJyY2xvbmVzYUByY2xvbmVvbmUtMjQ5ODE4LmlhbS5nc2VydmljZWFjY291bnQuY29tIiwic2NvcGUiOiJodHRwczovL3d3dy5nb29nbGVhcGlzLmNvbS9hdXRoL2RldnN0b3JhZ2UucmVhZF93cml0ZSIsImF1ZCI6Imh0dHBzOi8vb2F1dGgyLmdvb2dsZWFwaXMuY29tL3Rva2VuIiwiZXhwIjoxNTY2NTkwODQxLCJpYXQiOjE1NjY1ODcyNDF9.eKHnYITMOePVxO9F_zVUQzAoOs5LaIUC6aLhrtaX_Mzo5MLH_003FiZbj1LzjhdpEF24ys4Dj3jjzjVGvimAR5Eh--OOMr98sEJYZMfLwiF2fUWagqZpjVLBK0UlfV0AzmyrKIXKETrL3m71-PGcWdzP94qaL2ar1RSngCHT1tt5dszZPbAgsDchg-gtDlzq2eP5u3y6ZX1UbLX-o81UuPpV71RoJdX3Uxr9mkKOopjKNuowm3PECzNHl_RKTPEQymOIYfCKDNi3akuqzzxTabpxrcBkpEcj_249VPaLO9LUuCqZDY4E3hp3Agt-wOCVjJA_aLwxqqj91vNghczvBA&grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Ajwt-bearer
2019/08/23 21:07:31 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2019/08/23 21:07:31 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2019/08/23 21:07:31 DEBUG : HTTP RESPONSE (req 0xc0000f0b00)
2019/08/23 21:07:31 DEBUG : HTTP/1.1 200 OK
Transfer-Encoding: chunked
Alt-Svc: quic=":443"; ma=2592000; v="46,43,39"
Cache-Control: private
Content-Type: application/json; charset=utf-8
Date: Fri, 23 Aug 2019 19:07:31 GMT
Server: scaffolding on HTTPServer2
Vary: Origin
Vary: X-Origin
Vary: Referer
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-Xss-Protection: 0
ca
{
"access_token": "ya29.c.ElptB1SBZbzK_7dGNHePv4qKCtOnBCuG4_wDssVoPNi136BvBTdIDhP_OQtgx0gh7dRwM-0--_D__oNL3rWac_U0dLo5z-AoQSpIOuXd9G3D1Er7ZT7-ZtCWFOo",
"expires_in": 3600,
"token_type": "Bearer"
}
0
2019/08/23 21:07:31 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2019/08/23 21:07:31 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2019/08/23 21:07:31 DEBUG : HTTP REQUEST (req 0xc00018bd00)
2019/08/23 21:07:31 DEBUG : GET /storage/v1/b/rclonestore/o/SMALLFILE%20%2831%29.txt?alt=json&prettyPrint=false HTTP/1.1
Host: www.googleapis.com
User-Agent: rclone/v1.48.0-227-g077b4532-beta
Authorization: XXXX
Accept-Encoding: gzip
2019/08/23 21:07:31 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2019/08/23 21:07:31 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2019/08/23 21:07:31 DEBUG : HTTP RESPONSE (req 0xc00018bd00)
2019/08/23 21:07:31 DEBUG : HTTP/1.1 200 OK
Content-Length: 762
Alt-Svc: quic=":443"; ma=2592000; v="46,43,39"
Cache-Control: private, max-age=0, must-revalidate, no-transform
Content-Type: application/json; charset=UTF-8
Date: Fri, 23 Aug 2019 19:07:31 GMT
Etag: CPyA7O7Ml+QCEAE=
Expires: Fri, 23 Aug 2019 19:07:31 GMT
Server: UploadServer
Vary: Origin
Vary: X-Origin
X-Guploader-Uploadid: AEnB2UrxKdtgoLO_0k7rnWYfeLgDOJ7dQzONKQs3DA6b-yFof98Clhm1n6Iimd-nZw0CYDRUvL4Cn4GWJFt9um5iYfXwyVJfugOHlodcnt_0c-PPNfqaXiQ
{"kind":"storage#object","id":"rclonestore/SMALLFILE (31).txt/1566515465486460","selfLink":"https://www.googleapis.com/storage/v1/b/rclonestore/o/SMALLFILE%20(31).txt","name":"SMALLFILE (31).txt","bucket":"rclonestore","generation":"1566515465486460","metageneration":"1","contentType":"text/plain; charset=utf-8","timeCreated":"2019-08-22T23:11:05.486Z","updated":"2019-08-22T23:11:05.486Z","storageClass":"REGIONAL","timeStorageClassUpdated":"2019-08-22T23:11:05.486Z","size":"408","md5Hash":"rJOdAMRAeOfmEOcwombg9w==","mediaLink":"https://www.googleapis.com/download/storage/v1/b/rclonestore/o/SMALLFILE%20(31).txt?generation=1566515465486460&alt=media","metadata":{"mtime":"2019-08-23T01:11:05.316919500+02:00"},"crc32c":"/QE6Lw==","etag":"CPyA7O7Ml+QCEAE="}
2019/08/23 21:07:31 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2019/08/23 21:07:31 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2019/08/23 21:07:31 DEBUG : HTTP REQUEST (req 0xc00018b100)
2019/08/23 21:07:31 DEBUG : PATCH /storage/v1/b/rclonestore/o/SMALLFILE%20%2831%29.txt?alt=json&prettyPrint=false HTTP/1.1
Host: www.googleapis.com
User-Agent: rclone/v1.48.0-227-g077b4532-beta
Content-Length: 107
Authorization: XXXX
Content-Type: application/json
Accept-Encoding: gzip
{"bucket":"rclonestore","metadata":{"mtime":"1001-01-01T00:00:00.000000000Z"},"name":"SMALLFILE (31).txt"}
2019/08/23 21:07:31 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2019/08/23 21:07:31 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2019/08/23 21:07:31 DEBUG : HTTP RESPONSE (req 0xc00018b100)
2019/08/23 21:07:31 DEBUG : HTTP/1.1 403 Forbidden
Content-Length: 160
Alt-Svc: quic=":443"; ma=2592000; v="46,43,39"
Content-Type: application/json; charset=UTF-8
Date: Fri, 23 Aug 2019 19:07:31 GMT
Server: UploadServer
Vary: Origin
Vary: X-Origin
Www-Authenticate: Bearer realm="https://accounts.google.com/"
X-Guploader-Uploadid: AEnB2UrLW81byCL1BBgFMVWSGbjlVZFWW1C5PdKjHysTueyLd9ObZ7rAzHmaEDdlWOxbJU7A5KSLxTBnzG4lOtJgwGl4jB1ifA
{"error":{"errors":[{"domain":"global","reason":"insufficientPermissions","message":"Insufficient Permission"}],"code":403,"message":"Insufficient Permission"}}
2019/08/23 21:07:31 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2019/08/23 21:07:31 ERROR : Attempt 1/3 failed with 1 errors and: touch: couldn't set mod time: googleapi: Error 403: Insufficient Permission, insufficientPermissions
2019/08/23 21:07:31 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2019/08/23 21:07:31 DEBUG : HTTP REQUEST (req 0xc00051f600)
2019/08/23 21:07:31 DEBUG : GET /storage/v1/b/rclonestore/o/SMALLFILE%20%2831%29.txt?alt=json&prettyPrint=false HTTP/1.1
Host: www.googleapis.com
User-Agent: rclone/v1.48.0-227-g077b4532-beta
Authorization: XXXX
Accept-Encoding: gzip
2019/08/23 21:07:31 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2019/08/23 21:07:31 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2019/08/23 21:07:31 DEBUG : HTTP RESPONSE (req 0xc00051f600)
2019/08/23 21:07:31 DEBUG : HTTP/1.1 200 OK
Content-Length: 762
Alt-Svc: quic=":443"; ma=2592000; v="46,43,39"
Cache-Control: private, max-age=0, must-revalidate, no-transform
Content-Type: application/json; charset=UTF-8
Date: Fri, 23 Aug 2019 19:07:31 GMT
Etag: CPyA7O7Ml+QCEAE=
Expires: Fri, 23 Aug 2019 19:07:31 GMT
Server: UploadServer
Vary: Origin
Vary: X-Origin
X-Guploader-Uploadid: AEnB2UpjdGIOBnhJRznuEf1qXOSd1OoU5lc47KwpC7XNvTmRctAjEzir3wlH0-GK_0J2W52n7XDiRWnxCXfiEcMwLB0knPPvaiCmRjmeRkO-F_rBSsifeeA
{"kind":"storage#object","id":"rclonestore/SMALLFILE (31).txt/1566515465486460","selfLink":"https://www.googleapis.com/storage/v1/b/rclonestore/o/SMALLFILE%20(31).txt","name":"SMALLFILE (31).txt","bucket":"rclonestore","generation":"1566515465486460","metageneration":"1","contentType":"text/plain; charset=utf-8","timeCreated":"2019-08-22T23:11:05.486Z","updated":"2019-08-22T23:11:05.486Z","storageClass":"REGIONAL","timeStorageClassUpdated":"2019-08-22T23:11:05.486Z","size":"408","md5Hash":"rJOdAMRAeOfmEOcwombg9w==","mediaLink":"https://www.googleapis.com/download/storage/v1/b/rclonestore/o/SMALLFILE%20(31).txt?generation=1566515465486460&alt=media","metadata":{"mtime":"2019-08-23T01:11:05.316919500+02:00"},"crc32c":"/QE6Lw==","etag":"CPyA7O7Ml+QCEAE="}
2019/08/23 21:07:31 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2019/08/23 21:07:31 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2019/08/23 21:07:31 DEBUG : HTTP REQUEST (req 0xc0000f0b00)
2019/08/23 21:07:31 DEBUG : PATCH /storage/v1/b/rclonestore/o/SMALLFILE%20%2831%29.txt?alt=json&prettyPrint=false HTTP/1.1
Host: www.googleapis.com
User-Agent: rclone/v1.48.0-227-g077b4532-beta
Content-Length: 107
Authorization: XXXX
Content-Type: application/json
Accept-Encoding: gzip
{"bucket":"rclonestore","metadata":{"mtime":"1001-01-01T00:00:00.000000000Z"},"name":"SMALLFILE (31).txt"}
2019/08/23 21:07:31 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2019/08/23 21:07:32 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2019/08/23 21:07:32 DEBUG : HTTP RESPONSE (req 0xc0000f0b00)
2019/08/23 21:07:32 DEBUG : HTTP/1.1 403 Forbidden
Content-Length: 160
Alt-Svc: quic=":443"; ma=2592000; v="46,43,39"
Content-Type: application/json; charset=UTF-8
Date: Fri, 23 Aug 2019 19:07:31 GMT
Server: UploadServer
Vary: Origin
Vary: X-Origin
Www-Authenticate: Bearer realm="https://accounts.google.com/"
X-Guploader-Uploadid: AEnB2Uq9JIoKDH4KgvGyEMqyINzdxP92PEDV5omE5IVaL0KQTunvqa0Sre4G-bgeukPS1Z1GjTx8xn-7QrvDEA2PV-hpsNt3VfjcO4d_LLGTRjk-XDugO10
{"error":{"errors":[{"domain":"global","reason":"insufficientPermissions","message":"Insufficient Permission"}],"code":403,"message":"Insufficient Permission"}}
2019/08/23 21:07:32 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2019/08/23 21:07:32 ERROR : Attempt 2/3 failed with 1 errors and: touch: couldn't set mod time: googleapi: Error 403: Insufficient Permission, insufficientPermissions
2019/08/23 21:07:32 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2019/08/23 21:07:32 DEBUG : HTTP REQUEST (req 0xc00051fe00)
2019/08/23 21:07:32 DEBUG : GET /storage/v1/b/rclonestore/o/SMALLFILE%20%2831%29.txt?alt=json&prettyPrint=false HTTP/1.1
Host: www.googleapis.com
User-Agent: rclone/v1.48.0-227-g077b4532-beta
Authorization: XXXX
Accept-Encoding: gzip
2019/08/23 21:07:32 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2019/08/23 21:07:32 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2019/08/23 21:07:32 DEBUG : HTTP RESPONSE (req 0xc00051fe00)
2019/08/23 21:07:32 DEBUG : HTTP/1.1 200 OK
Content-Length: 762
Alt-Svc: quic=":443"; ma=2592000; v="46,43,39"
Cache-Control: private, max-age=0, must-revalidate, no-transform
Content-Type: application/json; charset=UTF-8
Date: Fri, 23 Aug 2019 19:07:32 GMT
Etag: CPyA7O7Ml+QCEAE=
Expires: Fri, 23 Aug 2019 19:07:32 GMT
Server: UploadServer
Vary: Origin
Vary: X-Origin
X-Guploader-Uploadid: AEnB2UpRDTyj317iXjtQjAYVVKkGXeEvniLwCkMtL1GAU198SQGnmdcpXSBX_dUE6epIYgcj5XHL7Rn7DRZ1mhmuyL2bBQ2UCfvA-FsoZYEN9FG4pj3-xwU
{"kind":"storage#object","id":"rclonestore/SMALLFILE (31).txt/1566515465486460","selfLink":"https://www.googleapis.com/storage/v1/b/rclonestore/o/SMALLFILE%20(31).txt","name":"SMALLFILE (31).txt","bucket":"rclonestore","generation":"1566515465486460","metageneration":"1","contentType":"text/plain; charset=utf-8","timeCreated":"2019-08-22T23:11:05.486Z","updated":"2019-08-22T23:11:05.486Z","storageClass":"REGIONAL","timeStorageClassUpdated":"2019-08-22T23:11:05.486Z","size":"408","md5Hash":"rJOdAMRAeOfmEOcwombg9w==","mediaLink":"https://www.googleapis.com/download/storage/v1/b/rclonestore/o/SMALLFILE%20(31).txt?generation=1566515465486460&alt=media","metadata":{"mtime":"2019-08-23T01:11:05.316919500+02:00"},"crc32c":"/QE6Lw==","etag":"CPyA7O7Ml+QCEAE="}
2019/08/23 21:07:32 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2019/08/23 21:07:32 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2019/08/23 21:07:32 DEBUG : HTTP REQUEST (req 0xc000312300)
2019/08/23 21:07:32 DEBUG : PATCH /storage/v1/b/rclonestore/o/SMALLFILE%20%2831%29.txt?alt=json&prettyPrint=false HTTP/1.1
Host: www.googleapis.com
User-Agent: rclone/v1.48.0-227-g077b4532-beta
Content-Length: 107
Authorization: XXXX
Content-Type: application/json
Accept-Encoding: gzip
{"bucket":"rclonestore","metadata":{"mtime":"1001-01-01T00:00:00.000000000Z"},"name":"SMALLFILE (31).txt"}
2019/08/23 21:07:32 DEBUG : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
2019/08/23 21:07:32 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2019/08/23 21:07:32 DEBUG : HTTP RESPONSE (req 0xc000312300)
2019/08/23 21:07:32 DEBUG : HTTP/1.1 403 Forbidden
Content-Length: 160
Alt-Svc: quic=":443"; ma=2592000; v="46,43,39"
Content-Type: application/json; charset=UTF-8
Date: Fri, 23 Aug 2019 19:07:32 GMT
Server: UploadServer
Vary: Origin
Vary: X-Origin
Www-Authenticate: Bearer realm="https://accounts.google.com/"
X-Guploader-Uploadid: AEnB2UoiH08zByORz-OVe1_3qholW7qcf41fS2wLlrKsgRYmltJDmYglnaIiwQ6mq5TBrA2tobY-511ofrJyrULQa5Tm_Vqr20idoPaeJFvzpq28wZXo8xU
{"error":{"errors":[{"domain":"global","reason":"insufficientPermissions","message":"Insufficient Permission"}],"code":403,"message":"Insufficient Permission"}}
2019/08/23 21:07:32 DEBUG : <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
2019/08/23 21:07:32 ERROR : Attempt 3/3 failed with 1 errors and: touch: couldn't set mod time: googleapi: Error 403: Insufficient Permission, insufficientPermissions
2019/08/23 21:07:32 Failed to touch: touch: couldn't set mod time: googleapi: Error 403: Insufficient Permission, insufficientPermissions