I had similar issues as well when I had the High DPI support setting for the editor activated, which I did because some parts of it are rather tiny on a 15" laptop at 2560x1600.
The weird thing about it was that it didn’t always happen. Sometimes when a second window (for example settings) opened it displayed just fine.
Eventually I turned the High DPI setting of again because the scaling factor (which I couldn’t find a setting for) was just too much.
The global scaling is set to 100%, so no upscaling from there. I did have it at 125% for a while but turned it down because there were scaling issues as well.
It seems that the best option might be to set the desktop to scale up on its own and have any scaling turned off inside UE…
(Note that I’m running LMDE with a KDE desktop, so some things might differ from Windows)