I have this issue and found this thread today. I'm using a folder that is syncing, maybe network shares, onedrive, synology drive, or dropbox can all cause similar issues. It mostly happened when I tried to save two changes rapidly in a row. Maybe an unlikely root cause for OP, who checked for other handlers, but might be affecting others facing this.
After one collision where it can't save if I try again too quickly all of Geany crashes on Windows 11. Never encountered this on Windows 10 for whatever reason.