Hi Ole,
Apologies for the radio silence the past couple of days - I was off for New Year's but back now and finally back at my proper workstation now! 
Here's the output from this test. Interestingly, this time the error occured as early as when using the first mkdir command. Do you spot anything from the debug logs?
Commands used
root@danserver:~# cd /mnt/odr-bkp/
root@danserver:/mnt/odr-bkp# mkdir test
root@danserver:/mnt/odr-bkp# cd test
root@danserver:/mnt/odr-bkp/test# echo "test" > testfile.txt
root@danserver:/mnt/odr-bkp/test# cat testfile.txt
test
root@danserver:/mnt/odr-bkp/test# cd ..
root@danserver:/mnt/odr-bkp# rm -rf test
Debug output
dan@danserver:~$ sudo rclone mount onedrive_bkp:srv_backup /mnt/odr-bkp --vfs-cache-mode writes -vv --log-format=time,microseconds
07:49:24.738538 DEBUG : rclone: Version "v1.61.1" starting with parameters ["rclone" "mount" "onedrive_bkp:srv_backup" "/mnt/odr-bkp" "--vfs-cache-mode" "writes" "-vv" "--log-format=time,microseconds"]
07:49:24.738782 DEBUG : Creating backend with remote "onedrive_bkp:srv_backup"
07:49:24.738877 DEBUG : Using config file from "/root/.config/rclone/rclone.conf"
07:49:25.269970 DEBUG : OneDrive root 'srv_backup': Next delta token is: aTE09NjM4MDgzOTgwNzEzNzM7SUQ9QzAwNEI4RTRBMjgxMDkwMCExMDc7TFI9NjM4MDg0MTE3NjUyNDM7RVA9MjA7U0k9MjI7RExFUD0wO1NHPTE7U089NjtQST0z
07:49:25.270049 DEBUG : vfs cache: root is "/root/.cache/rclone"
07:49:25.270097 DEBUG : vfs cache: data root is "/root/.cache/rclone/vfs/onedrive_bkp/srv_backup"
07:49:25.270106 DEBUG : vfs cache: metadata root is "/root/.cache/rclone/vfsMeta/onedrive_bkp/srv_backup"
07:49:25.270112 DEBUG : Creating backend with remote "/root/.cache/rclone/vfs/onedrive_bkp/srv_backup"
07:49:25.270292 DEBUG : Creating backend with remote "/root/.cache/rclone/vfsMeta/onedrive_bkp/srv_backup"
07:49:25.270856 DEBUG : OneDrive root 'srv_backup': Mounting on "/mnt/odr-bkp"
07:49:25.270983 INFO : vfs cache: cleaned: objects 0 (was 0) in use 0, to upload 0, uploading 0, total size 0 (was 0)
07:49:25.272727 DEBUG : : Root:
07:49:25.272780 DEBUG : : >Root: node=/, err=<nil>
07:50:25.271106 INFO : vfs cache: cleaned: objects 0 (was 0) in use 0, to upload 0, uploading 0, total size 0 (was 0)
07:50:25.271180 DEBUG : OneDrive root 'srv_backup': Checking for changes on remote
07:50:54.072222 DEBUG : /: Attr:
07:50:54.072320 DEBUG : /: >Attr: attr=valid=1s ino=0 size=0 mode=drwxr-xr-x, err=<nil>
07:50:55.456927 DEBUG : /: Attr:
07:50:55.456965 DEBUG : /: >Attr: attr=valid=1s ino=0 size=0 mode=drwxr-xr-x, err=<nil>
07:51:11.268389 DEBUG : /: Attr:
07:51:11.268427 DEBUG : /: >Attr: attr=valid=1s ino=0 size=0 mode=drwxr-xr-x, err=<nil>
07:51:11.269902 DEBUG : /: Lookup: name="test"
07:51:11.424851 DEBUG : /: >Lookup: node=<nil>, err=no such file or directory
07:51:11.425058 DEBUG : /: Mkdir: name="test"
07:51:11.810791 DEBUG : : Added virtual directory entry vAddDir: "test"
07:51:11.810838 DEBUG : /: >Mkdir: node=test/, err=<nil>
07:51:11.810876 DEBUG : test/: Attr:
07:51:11.810903 DEBUG : test/: >Attr: attr=valid=1s ino=0 size=0 mode=drwxr-xr-x, err=<nil>
07:51:25.270170 DEBUG : OneDrive root 'srv_backup': Checking for changes on remote
07:51:25.271683 INFO : vfs cache: cleaned: objects 0 (was 0) in use 0, to upload 0, uploading 0, total size 0 (was 0)
07:51:25.493716 ERROR : OneDrive root 'srv_backup': Could not get item full path: invalid parent path: /Livefolders
07:51:25.493743 ERROR : OneDrive root 'srv_backup': Could not get item full path: invalid parent path: /Livefolders/srv_backup
07:51:54.740277 DEBUG : /: Attr:
07:51:54.740321 DEBUG : /: >Attr: attr=valid=1s ino=0 size=0 mode=drwxr-xr-x, err=<nil>
07:51:54.740518 DEBUG : test/: Attr:
07:51:54.740530 DEBUG : test/: >Attr: attr=valid=1s ino=0 size=0 mode=drwxr-xr-x, err=<nil>
07:52:25.270297 DEBUG : OneDrive root 'srv_backup': Checking for changes on remote
07:52:25.271228 INFO : vfs cache: cleaned: objects 0 (was 0) in use 0, to upload 0, uploading 0, total size 0 (was 0)
07:52:51.833381 DEBUG : test/: Lookup: name="testfile.txt"
07:52:52.041379 DEBUG : test/: >Lookup: node=<nil>, err=no such file or directory
07:52:52.041598 DEBUG : test/: Create: name="testfile.txt"
07:52:52.041631 DEBUG : test/testfile.txt: Open: flags=O_WRONLY|O_CREATE|O_TRUNC
07:52:52.041724 DEBUG : test/testfile.txt: newRWFileHandle:
07:52:52.041751 DEBUG : test/testfile.txt(0xc0002da240): openPending:
07:52:52.041968 DEBUG : test/testfile.txt: vfs cache: truncate to size=0 (not needed as size correct)
07:52:52.042219 DEBUG : test: Added virtual directory entry vAddFile: "testfile.txt"
07:52:52.042234 DEBUG : test/testfile.txt(0xc0002da240): >openPending: err=<nil>
07:52:52.042376 DEBUG : test/testfile.txt: >newRWFileHandle: err=<nil>
07:52:52.042393 DEBUG : test: Added virtual directory entry vAddFile: "testfile.txt"
07:52:52.042426 DEBUG : test/testfile.txt: >Open: fd=test/testfile.txt (rw), err=<nil>
07:52:52.042459 DEBUG : test/: >Create: node=test/testfile.txt, handle=&{test/testfile.txt (rw)}, err=<nil>
07:52:52.042475 DEBUG : test/testfile.txt: Attr:
07:52:52.042501 DEBUG : test/testfile.txt: >Attr: a=valid=1s ino=0 size=0 mode=-rw-r--r--, err=<nil>
07:52:52.042765 DEBUG : &{test/testfile.txt (rw)}: Flush:
07:52:52.042791 DEBUG : test/testfile.txt(0xc0002da240): RWFileHandle.Flush
07:52:52.042807 DEBUG : &{test/testfile.txt (rw)}: >Flush: err=<nil>
07:52:52.043169 DEBUG : &{test/testfile.txt (rw)}: Write: len=5, offset=0
07:52:52.043191 DEBUG : test/testfile.txt(0xc0002da240): _writeAt: size=5, off=0
07:52:52.043241 DEBUG : test/testfile.txt(0xc0002da240): >_writeAt: n=5, err=<nil>
07:52:52.043268 DEBUG : &{test/testfile.txt (rw)}: >Write: written=5, err=<nil>
07:52:52.043363 DEBUG : &{test/testfile.txt (rw)}: Flush:
07:52:52.043377 DEBUG : test/testfile.txt(0xc0002da240): RWFileHandle.Flush
07:52:52.043383 DEBUG : &{test/testfile.txt (rw)}: >Flush: err=<nil>
07:52:52.043527 DEBUG : &{test/testfile.txt (rw)}: Release:
07:52:52.043535 DEBUG : test/testfile.txt(0xc0002da240): RWFileHandle.Release
07:52:52.043542 DEBUG : test/testfile.txt(0xc0002da240): close:
07:52:52.043769 DEBUG : test/testfile.txt: vfs cache: setting modification time to 2023-01-04 07:52:52.043232206 +0100 CET m=+207.334654180
07:52:52.043793 INFO : test/testfile.txt: vfs cache: queuing for upload in 5s
07:52:52.043807 DEBUG : test/testfile.txt(0xc0002da240): >close: err=<nil>
07:52:52.043813 DEBUG : &{test/testfile.txt (rw)}: >Release: err=<nil>
07:52:57.044012 DEBUG : test/testfile.txt: vfs cache: starting upload
07:52:57.044359 DEBUG : test/testfile.txt: Starting multipart upload
07:52:57.184010 DEBUG : test/testfile.txt: Uploading segment 0/5 size 5
07:52:57.792082 DEBUG : test/testfile.txt: sha1 = 4e1243bd22c66e76c2ba9eddc1f91394e57f9f83 OK
07:52:57.792115 INFO : test/testfile.txt: Copied (new)
07:52:57.792147 DEBUG : test/testfile.txt: vfs cache: fingerprint now "5,2023-01-04 06:52:52 +0000 UTC,4e1243bd22c66e76c2ba9eddc1f91394e57f9f83"
07:52:57.792155 DEBUG : test/testfile.txt: vfs cache: writeback object to VFS layer
07:52:57.792165 DEBUG : test: Added virtual directory entry vAddFile: "testfile.txt"
07:52:57.792383 INFO : test/testfile.txt: vfs cache: upload succeeded try #1
07:53:25.271436 DEBUG : OneDrive root 'srv_backup': Checking for changes on remote
07:53:25.271715 DEBUG : vfs cache RemoveNotInUse (maxAge=3600000000000, emptyOnly=false): item test/testfile.txt not removed, freed 0 bytes
07:53:25.271755 INFO : vfs cache: cleaned: objects 1 (was 1) in use 0, to upload 0, uploading 0, total size 5 (was 5)
07:53:25.423197 ERROR : OneDrive root 'srv_backup': Could not get item full path: invalid parent path: /Livefolders
07:53:25.423272 ERROR : OneDrive root 'srv_backup': Could not get item full path: invalid parent path: /Livefolders/srv_backup
07:53:25.423286 ERROR : OneDrive root 'srv_backup': Could not get item full path: invalid parent path: /Livefolders/srv_backup/test
07:53:35.782947 DEBUG : test/: Attr:
07:53:35.782992 DEBUG : test/: >Attr: attr=valid=1s ino=0 size=0 mode=drwxr-xr-x, err=<nil>
07:53:35.784299 DEBUG : test/testfile.txt: Open: flags=OpenReadOnly
07:53:35.784315 DEBUG : test/testfile.txt: Open: flags=O_RDONLY
07:53:35.784346 DEBUG : test/testfile.txt: newRWFileHandle:
07:53:35.784353 DEBUG : test/testfile.txt: >newRWFileHandle: err=<nil>
07:53:35.784358 DEBUG : test/testfile.txt: >Open: fd=test/testfile.txt (rw), err=<nil>
07:53:35.784368 DEBUG : test/testfile.txt: >Open: fh=&{test/testfile.txt (rw)}, err=<nil>
07:53:35.784478 DEBUG : test/testfile.txt: Attr:
07:53:35.784525 DEBUG : test/testfile.txt: >Attr: a=valid=1s ino=0 size=5 mode=-rw-r--r--, err=<nil>
07:53:35.784625 DEBUG : &{test/testfile.txt (rw)}: Read: len=4096, offset=0
07:53:35.784637 DEBUG : test/testfile.txt(0xc0002da180): _readAt: size=4096, off=0
07:53:35.784653 DEBUG : test/testfile.txt(0xc0002da180): openPending:
07:53:35.784694 DEBUG : test/testfile.txt: vfs cache: checking remote fingerprint "5,2023-01-04 06:52:52 +0000 UTC,4e1243bd22c66e76c2ba9eddc1f91394e57f9f83" against cached fingerprint "5,2023-01-04 06:52:52 +0000 UTC,4e1243bd22c66e76c2ba9eddc1f91394e57f9f83"
07:53:35.784724 DEBUG : test/testfile.txt: vfs cache: truncate to size=5 (not needed as size correct)
07:53:35.784898 DEBUG : test: Added virtual directory entry vAddFile: "testfile.txt"
07:53:35.784905 DEBUG : test/testfile.txt(0xc0002da180): >openPending: err=<nil>
07:53:35.784922 DEBUG : vfs cache: looking for range={Pos:0 Size:5} in [{Pos:0 Size:5}] - present true
07:53:35.784941 DEBUG : test/testfile.txt(0xc0002da180): >_readAt: n=5, err=EOF
07:53:35.784960 DEBUG : &{test/testfile.txt (rw)}: >Read: read=5, err=<nil>
07:53:35.785111 DEBUG : &{test/testfile.txt (rw)}: Flush:
07:53:35.785130 DEBUG : test/testfile.txt(0xc0002da180): RWFileHandle.Flush
07:53:35.785138 DEBUG : &{test/testfile.txt (rw)}: >Flush: err=<nil>
07:53:35.785318 DEBUG : &{test/testfile.txt (rw)}: Release:
07:53:35.785336 DEBUG : test/testfile.txt(0xc0002da180): RWFileHandle.Release
07:53:35.785342 DEBUG : test/testfile.txt(0xc0002da180): close:
07:53:35.785622 DEBUG : test/testfile.txt: vfs cache: setting modification time to 2023-01-04 06:52:52 +0000 UTC
07:53:35.785634 DEBUG : test/testfile.txt(0xc0002da180): >close: err=<nil>
07:53:35.785639 DEBUG : &{test/testfile.txt (rw)}: >Release: err=<nil>
07:54:01.709729 DEBUG : /: Attr:
07:54:01.709762 DEBUG : /: >Attr: attr=valid=1s ino=0 size=0 mode=drwxr-xr-x, err=<nil>
07:54:01.709856 DEBUG : /: Lookup: name="test"
07:54:01.709868 DEBUG : /: >Lookup: node=test/, err=<nil>
07:54:01.709872 DEBUG : test/: Attr:
07:54:01.709881 DEBUG : test/: >Attr: attr=valid=1s ino=0 size=0 mode=drwxr-xr-x, err=<nil>
07:54:25.271008 DEBUG : OneDrive root 'srv_backup': Checking for changes on remote
07:54:25.271171 DEBUG : vfs cache RemoveNotInUse (maxAge=3600000000000, emptyOnly=false): item test/testfile.txt not removed, freed 0 bytes
07:54:25.271191 INFO : vfs cache: cleaned: objects 1 (was 1) in use 0, to upload 0, uploading 0, total size 5 (was 5)
07:54:39.429504 DEBUG : /: Attr:
07:54:39.429550 DEBUG : /: >Attr: attr=valid=1s ino=0 size=0 mode=drwxr-xr-x, err=<nil>
07:54:39.430492 DEBUG : /: Lookup: name="test"
07:54:39.430505 DEBUG : /: >Lookup: node=test/, err=<nil>
07:54:39.430514 DEBUG : test/: Attr:
07:54:39.430520 DEBUG : test/: >Attr: attr=valid=1s ino=0 size=0 mode=drwxr-xr-x, err=<nil>
07:54:39.430692 DEBUG : test/: ReadDirAll:
07:54:39.430708 DEBUG : test/: >ReadDirAll: item=3, err=<nil>
07:54:39.430907 DEBUG : test/: Attr:
07:54:39.430918 DEBUG : test/: >Attr: attr=valid=1s ino=0 size=0 mode=drwxr-xr-x, err=<nil>
07:54:39.431014 DEBUG : test/: ReadDirAll:
07:54:39.431025 DEBUG : test/: >ReadDirAll: item=3, err=<nil>
07:54:39.431139 DEBUG : test/: Lookup: name="testfile.txt"
07:54:39.431149 DEBUG : test/: >Lookup: node=test/testfile.txt, err=<nil>
07:54:39.431157 DEBUG : test/testfile.txt: Attr:
07:54:39.431167 DEBUG : test/testfile.txt: >Attr: a=valid=1s ino=0 size=5 mode=-rw-r--r--, err=<nil>
07:54:39.431221 DEBUG : test/: Remove: name="testfile.txt"
07:54:39.431229 DEBUG : test/testfile.txt: Remove:
07:54:39.431356 INFO : test/testfile.txt: vfs cache: removed cache file as file deleted
07:54:39.431384 DEBUG : test/testfile.txt: vfs cache: removed metadata from cache as file deleted
07:54:39.431390 DEBUG : test: Added virtual directory entry vDel: "testfile.txt"
07:54:39.679198 DEBUG : test/testfile.txt: >Remove: err=<nil>
07:54:39.679239 DEBUG : test/: >Remove: err=<nil>
07:54:39.679482 DEBUG : /: Remove: name="test"
07:54:40.075187 DEBUG : : Added virtual directory entry vDel: "test"
07:54:40.075215 DEBUG : /: >Remove: err=<nil>