The same thing happened. Here's a censored version of the end of the log (nothing interesting in the log before these lines):
2019/09/05 14:58:34 DEBUG : 096.jpg: Unchanged skipping
2019/09/05 14:58:34 DEBUG : 097.jpg: Unchanged skipping
2019/09/05 14:58:34 DEBUG : 098.jpg: Unchanged skipping
2019/09/05 14:58:34 DEBUG : 099.jpg: Unchanged skipping
2019/09/05 14:58:34 DEBUG : 114.jpg: Size and modification time the same (differ by 0s, within tolerance 1ms)
2019/09/05 14:58:34 DEBUG : 114.jpg: Unchanged skipping
2019/09/05 14:58:34 DEBUG : 122.jpg: Size and modification time the same (differ by 0s, within tolerance 1ms)
2019/09/05 14:58:34 DEBUG : 122.jpg: Unchanged skipping
2019/09/05 14:58:38 INFO : file.class: Copied (new)
2019/09/05 14:58:38 INFO : file.sol: Copied (new)
2019/09/05 14:58:38 ERROR : file.png: Failed to copy: file already closed
2019/09/05 14:58:38 DEBUG : pacer: low level retry 1/1 (error googleapi: Error 403: User Rate Limit Exceeded. Rate of requests for user exceed configured project quota. You may consider re-evaluating expected per-user traffic to the API and adjust project quota limits accordingly. You may monitor aggregate quota usage and adjust limits in the API Console: https://console.developers.google.com/apis/api/drive.googleapis.com/quotas, userRateLimitExceeded)
2019/09/05 14:58:38 DEBUG : pacer: Rate limited, increasing sleep to 1.566995453s
2019/09/05 14:58:38 DEBUG : file.class: Received error: googleapi: Error 403: User Rate Limit Exceeded. Rate of requests for user exceed configured project quota. You may consider re-evaluating expected per-user traffic to the API and adjust project quota limits accordingly. You may monitor aggregate quota usage and adjust limits in the API Console: https://console.developers.google.com/apis/api/drive.googleapis.com/quotas, userRateLimitExceeded - low level retry 1/10
2019/09/05 14:58:38 DEBUG : pacer: Reducing sleep to 0s
2019/09/05 14:58:38 DEBUG : pacer: low level retry 1/1 (error googleapi: Error 403: User Rate Limit Exceeded. Rate of requests for user exceed configured project quota. You may consider re-evaluating expected per-user traffic to the API and adjust project quota limits accordingly. You may monitor aggregate quota usage and adjust limits in the API Console: https://console.developers.google.com/apis/api/drive.googleapis.com/quotas, userRateLimitExceeded)
2019/09/05 14:58:38 DEBUG : pacer: Rate limited, increasing sleep to 1.079814704s
2019/09/05 14:58:38 DEBUG : file.class: Received error: googleapi: Error 403: User Rate Limit Exceeded. Rate of requests for user exceed configured project quota. You may consider re-evaluating expected per-user traffic to the API and adjust project quota limits accordingly. You may monitor aggregate quota usage and adjust limits in the API Console: https://console.developers.google.com/apis/api/drive.googleapis.com/quotas, userRateLimitExceeded - low level retry 1/10
2019/09/05 14:58:38 DEBUG : pacer: low level retry 1/10 (error googleapi: Error 403: User Rate Limit Exceeded. Rate of requests for user exceed configured project quota. You may consider re-evaluating expected per-user traffic to the API and adjust project quota limits accordingly. You may monitor aggregate quota usage and adjust limits in the API Console: https://console.developers.google.com/apis/api/drive.googleapis.com/quotas, userRateLimitExceeded)
2019/09/05 14:58:38 DEBUG : pacer: Rate limited, increasing sleep to 2.566992179s
2019/09/05 14:58:39 DEBUG : pacer: Reducing sleep to 0s
2019/09/05 14:58:39 INFO : file.jpg: Copied (new)
2019/09/05 14:58:39 INFO : file.m4a: Copied (new)
I just keyboard-interrupted the command again as it was stuck on this for an hour:
Transferred: 42.207G / 125.084 GBytes, 34%, 5.845 MBytes/s, ETA 4h1m58s
Errors: 244 (retrying may help)
Checks: 528713 / 528713, 100%
Transferred: 20467 / 30497, 67%
Elapsed time: 2h3m13.8s
Transferring:
* <file>: 0% /1.661k, 0/s, -
* <file>: transferring
* <file>: 0% /1.247k, 0/s, -
* <file>: 0% /984, 0/s, -
* <file>: 0% /2.345k, 0/s, -
* <file>: 0% /1.928M, 0/s, -
* <file>:184% /57, 0/s, -
* <file>: transferring
* <file>: transferring^C
I've also never seen transferring like in three of these files. The log is over 200 MB in size since I ran it with -vv.