I got it fixed by uninstalling a recent program I had installed - Discord (a discussion platform). Everything works fine since I did that. There probably should be a list of programs which can cause problems with DOSBOX.

Fullscreen has stopped working for me. It flashes on and then reverts to a DOSBOX Status Screen. I have tried updating and rebooting, but nothing helps. The regular screen shows up in such miniature on my PC that I can't really use it. I am on a Windows 10 PC.