Striped background on starting Unreal

I updated my local copy of Unreal to 4.16.3 final, and now when I try to run the editor, I get a grey striped background and nothing happens. (see screenshot)

Hitting pause in VS shows that it is stuck in FEventWin::Wait, waiting for an event with EventId 23…

Does anyone have any idea what might be causing this? I never had anything like this before.

That looks like the main frame of the editor… we haven’t seen this issue for a while, but does this suggestion help at all?