User fonts being moved to (disabled) folder on OS update

Whenever I update the OS, (e.g. point updates to Sonoma, and yesterday upgrading to Sequoia 15.5), all my user fonts (in ~/Library/Fonts) get moved to a folder called Fonts (disabled), also in the user Library. The fonts are decent OTFs from Monotype, Adobe, Linotype etc. I have no reason to suspect that they are 'corrupt' in any way. If I move them back to the Fonts folder, they work perfectly. Font Book validates them with no errors, if that actually means anything. I don't have the problem on my other computer, with identical fonts. The file attributes and permissions are all the same. -rw-r--r--@ 1 Ben staff 54480 16 Aug 2010 CenturyStd.otf com.apple.provenance 11 Any idea how I can troubleshoot or fix this? I am still using Linotype's FontExplorerX font manager app (sadly discontinued a few years ago); but I don't think it's that because: it doesn't happen on the other Mac, which also runs it; the fonts get moved before the app launches; and it doesn't happen on a standard reboot, just an OS update. I have several fonts in /Library/Fonts/, too; but they are unaffected.