If Robocopy fails to copy a file (for any reason) it will retry up to 1 million times, waiting 30 seconds between each attempt.
Eventually, after 30 million seconds or about 1 year, robocopy will timeout and move on to the next file.
You can reduce the retry count with /r and shorten the wait time with /w.
E.g. robocopy c:\ d:\ /e /r:0 /w:0
This says: If you encounter an error, don't retry.
Robocopy Retry & Wait parameters:
The never ending error message you will see if a file can't be copied:
2018/02/06 09:19:13 ERROR 32 (0x00000020) Copying File .\sqlite3\db.lock The process cannot access the file because it is being used by another process. Waiting 30 seconds... Retrying... 2018/02/06 09:19:13 ERROR 32 (0x00000020) Copying File .\sqlite3\db.lock The process cannot access the file because it is being used by another process. Waiting 30 seconds... Retrying... 2018/02/06 09:19:43 ERROR 32 (0x00000020) Copying File .\sqlite3\db.lock The process cannot access the file because it is being used by another process. Waiting 30 seconds... Retrying...