There's a global limit on the number of sandbox extensions (security scoped bookmarks) open at once. If it fails that's because someone is leaking them.
Interesting. Maybe that's one of the reasons. I think there are multiple root causes. Another common issue I see is "failed to get app specific key"
Hitting the sandbox extension limit is not necessarily a leak. There are a number of apps that deal with thousands of files at once and they will very quickly hit the limits. It's a perennial problem with anyone who makes professional, but sandboxed, software for macOS.