I get 0 fps with a very simple level with the following: a 3d widget, a post processing material and mouse wiggling:
As you can see it completely freezes the fps when wiggling the mouse fast, the faster the mouse move the lower the fps. That post process material that is used you can see in the lower left. In the world outliner on the right you can see that there is just a actor called Testwidget which has just a simple 3d widget component.
Here is it with no post processing material:
From the gif it looks like it just the 3 vector component but there are other nodes in there that are not used. I tried a hour to find out how to recreate a post procress material that always recreates the bug but had no luck, sometimes the bug happened when I deleted nodes and sometimes when I added nodes. The only thing I can think of that it gets corrupted on compiling the material and that it happens more likely with lots of nodes in the material (and it doesn’t matter if the nodes are used or not). The very complex post material I use for the game I could not get working without the bug yet.
I also tried this with play as standalone game with the same result.