I've been having the same problem with many, many events. Several others have tried also with the same results. We've tried everything we can think of. Used different PCs, browsers, tried editing different events, etc. Whether creating a new event or editing an existing one, quick add New Event or Add Event Detail & Location, single event or repeating, entire location or with room reservations, NO location or even just bringing an event up, making NO changes and click Update Event - as long as there is another event in the same time, I have the problem...the hanging circular display. After several minutes we can press ESC and the editing screen re-appears.
The only work-around I've found is to create the event on Monday (no other events), save it and then drag it to the correct time.
What's wrong?