Thanks for bringing this up. It’s indeed a known limitation of the BSD file watching mechanism (kqueue). There’s no solution other than disabling filesystem watcher. We even once discussed doing that automatically on BSDs. Either on an arbitrary limit of items in a folder or just generally. I should probably get around to doing that, as it’s not nice to knowingly get users into a state that’s known to be problematic.
How many items (dirs and files) do you have in the affected folders?
Filed an issue to track it and as a reminder: Watching for changes using too many system resources on BSDs (kqueue) · Issue #7855 · syncthing/syncthing · GitHub