That sounds tough. I didn’t had similar problems. Probably only Michael can help.
What windows version are you using? e.g. win10 Pro ?H? Maybe that’s a useful info for Michael.
Could you try to move the complete qs program folder to another pc and try it there?
You could also try it with an “empty” .qucs folder (just rename .qucs into .qucs_old and create a new empty .qucs folder)
If that helps, you can populate the .qucs folder with the stuff from .qucs_old step by step and see when it fails