Sync .ffs_lock errors

[sgoffman]

My network backup started crapping out a couple of weeks ago (worked fine for years before that).

Backing up from Windows to a Synology DiskStation, I now get an error for each root folder being sync'd:
Warning Cannot set directory locks for the following folders:
Cannot write file "<destination root folder>\Delete.0.sync.ffs_lock".
ERROR_FILE_NOT_FOUND: The system cannot find the file specified. [CreateFile]

The listed files were all created, and still exist. If I manually delete them, the next backup run will create them again, then fail to delete them. If I don't manually delete them, the next backup will create "Delete.1.sync.ffs_lock", then "Delete.2.sync.ffs_lock", and so on, then report the "Cannot write file" error for each of them.

Additionally, every changed file fails to sync with the error:
Cannot write file "<Full destination filename>-0c86.ffs_tmp".
ERROR_FILE_NOT_FOUND: The system cannot find the file specified. [CreateFile]

Again, the ffs_tmp files listed were created, still exist, and I can manually delete them.

It seems like a permissions problem, but the users/permissions setup has not changed. Running as Administrator doesn't change anything.

Thanks for any suggestions on fixing this issue!

[xCSxXenon]

Reboot the NAS, check for drive health

[sgoffman]

Drive health all reported fine, but a reboot fixed it (can't believe I hadn't tried that). Thanks!

[xCSxXenon]

Anytime, it's usually just a network issue that "deadlocks" the connection so the access is "still there" but doesn't work