Q: Old encrypted files and folders are not reliably deleted.
A: If READABLE_NAMES=0, the file and folder names are encrypted. The problem is that BmuS deletes the files based on the folder name, which is composed of the backup date. BmuS does not delete based on the age of the file or the last modification date, as these timestamps may be younger than the original backup date.
If the folder names are encrypted, BmuS can no longer recognize the creation date of the folder. BmuS then falls back on checking the timestamp of the folder or file.
However, if this timestamp has been changed in the meantime by a third-party system (NAS), BmuS may not delete the file because the timestamp is not (yet) outside the interval defined in ENCRYPTED_BACKUP_AGE_DAYS.
Solution: (1) Either you wait until this is the case (which might be the day after) and hope that your NAS (or wherever these files are stored) no longer changes the timestamps, or (2) you have to manually delete the skipped folders and files.
In any case, the routine works reliably for encrypted and unencrypted folders and files that were created with READABLE_NAMES=1.