As Dietmar said, VS Code may cause this. Quite funny
to read, actually,
because we've been dealing with this issue for over a year, and
yesterday was the very first time Ceph complained about a client and we
saw VS Code's remote stuff running. Coincidence.
I'm holding my breath that the vscode issue is the one affecting us - I
got my users to tweak their vscode configs and the problem seemed to go
away, but I guess I won't consider it 'solved' until a few days pass
without it coming back... :)