Some time back a couple of us reported similar behaviour that seemed to be related to using Cloud storage.
Gradually eliminating connections helped to diagnose this. In my case, PaperPort Anywhere was implicated.
Directory Opus Resource Centre • View topic - Delays with PaperPort Anywhere cloud connector
There have been other discussions along similar lines:
Directory Opus Resource Centre • View topic - Frequent Lockups, empty tabs (iCloud related?)
This may have nothing to do with your problem. I just offer it as a way of eliminating issues.
I still see these "hangs" from time to time. But life's too short to chase them to earth.