As a result of BF-39204 we are seeing backups that are meant to be removed still present in the optionalFilesCopied listing, meaning that they were not restored if they needed to be. This looks like a testing issue where the backup took place after the file was dropped and recreated, so the files were expected to be restored but not present. 

Ensure the race is less likely with adding an extra pruning step, and additional logging if it happens again, since we need more information to make a concrete judgement here.