Warnings are logged in the Backup Client backup log that says "Could not move backup file to cache", for example:
Warning: 11:20:54 Could not move backup file to cache: E:\Data\File.txt, reason: Trying to move a file to the cache that does not exist (C:\Program Files\Attix5 Pro\Backup Client SE\toBackup\6F\6F11E147577A349A7ACAC9FE619CC947)
This has been seen during backups of network shares where the share goes down during the backup. This error is not critical at all and the only possible side-effect of this can be that with the next backup a full copy of the file will be transmitted instead of a patch, but only if the file has changed. If not then this will have no effect at all other than the warning logged.
There is currently no fix for this.