If you make some process snapshots of Opus while the problem is happening then we might be able to see what's going on, if something in our process is blocking or waiting on something.
Beyond that, I'm not sure we would be able to tell what they are waiting for on their side. It may be something they'll need to diagnose, whether the change needs to be on our side or theirs, since only they would be able to say for sure why their UI is still on the screen and what it's blocking on or waiting for.