Mission Control shrinks windows to single pixel size

I just noticed that when I activated Mission Control (Mojave on 2018 Mac mini with a 3840x1600 display), all the windows shrank down to a single pixel. It appears there have been a few conversation threads on this topic, but they're all old enough I cannot reply so have to make a new post. Hopefully my reply will get linked with those because I also discovered the solution in my case: I happened to be running the "Steam" application (from Valve), and when I quit that, Mission Control behaved properly. Thus it seems that some applications can break Mission Control's behaviour in some circumstances (wild speculation: I would guess it is related to the large screen size and how some applications maintain offscreen windows). If you're having this problem I suggest that you try to quit your running applications one-by-one to see if the problem goes away after closing a specific one (or more).