I got a new video card (1080 Ti) and loaded up Doomsday, tried it out to see how it played in some areas that lagged previously, found it to run much better, then exited.
I decided to restart it to try out another addon, and now it just makes the screen turn black for a few seconds, then crashes with the message "Doomsday.exe has stopped working".
Another thing I noticed is, I always run at 85Hz. Trying to run Doomsday forces 100Hz. Even the old 1.15.6 version of Doomsday (which still works) now forces my display to 100Hz.
I can only imagine Doomsday 2 munged it's settings file but I'm not sure where it's located.