I have experienced the same thing, Revit does not freeze, but it's like an invisible prompt blocks the access to the UI.
A temporary workaround for this, instead of ending the task and losing work:
1. Make sure the Revit window is your active window (by Alt+Tab / selecting it in taskbar)
2. Hold the Alt key to activate keyboard shortcuts in Revit, release Alt when numbers appear over the panel and quick access bar
3. Press whatever number Synchronize has (default is 3)
4. Press the Enter key to synchronize again.
Doing this should break the "stuck" window.
Hope this can help those who need the 2.8 for now.
Thanks a lot for sharing this with us.
I'm very afraid, there is no ETA just yet regarding when this will be resolved, we're still trying to figure out the cause behind this behavior - if there are any news soon I'll get back to you all.