So I've just recently got back into Stellaris and I've been getting these blank event windows popping up. I found a post on reddit that showing how to identify what the problem could be and it seems certain Titan event ID's are causing this to happen.

Using the debugtooltip is show me:
"Event ID titan_doomsday.102, .103, 104, .105, .199 and .808 all in their own separate event windows that will pop back up after clicking ok

At the moment these are having some type of trouble in my game. I'm about to unistall and see if that fixes the issue. I will update this post if it does or not.