Time Machine fails with repeated 'file xyz could not be backed up' errors

Today I tried to do a Time Machine backup to an external disk. I got an error message saying the backup failed because a file "could not be backed up". File name was /private/var/root/Library/Logs/Bluetooth/bluetoothd-hci-2025-03-13_19-23-02.pklg This file didn't seem to be essential, so I deleted the file and tried again. Got another error message of the same type complaining about another file. Lather, rinse, repeat a few more times and I got suspicious. Initially I assumed the error was saying the source file could not be read. I checked the files, and I could open them in a text editor. Permissions also didn't look odd. What's going on? Edit: The SSD is a Crucial X9 Pro. I found an Amazon review that contains this gem: > Crucial Support told me that APFS (case-sensitive) often does this with this device, but nowhere in their documentation nor sales literature do they state this