@grammarhag Sorry to hear you’re experiencing this really strange issue. Very odd to me that you and the other poster linked to above both started seeing these symptoms on about the same day.
I made two suggestions to the other poster, and I think you should try them as well.
Temporarily disable your antivirus or white list Scrivener.
Boot your PC into Safe Mode and see if Scrivener works normally.
Hopefully you can discover what’s the root cause of this.
Best,
Jim