It does not happen in troubleshooting mode. Moreover, in regular mode, it only happens in a group library, not in my main library. So what should I do next?
If it doesn't happen with all plugins disabled, you'll need to identify the plugin that's causing it and then report the problem to the plugin's developer.
If so, can you provide a Debug ID for reproducing it?
(By the way, I was wrong about this not happening in my main library; it happens there too.)