In my case, it wasn’t the files themselves, but a directory above the files (that had a mismatched case).
I understand your file have been unchanged and untouched or months. The parent directories, too? On a wild shot guess, could it be that the directories or files are being changed on the other peer sync computers and the error shows up on an innocent computer?
To debug, pick one error filename and check the full path and filename for any differences in case. Any difference?
In my case I found a difference and the error messages went away when I manually corrected the one errant directory to identical case.