It seems your suspicion was correct - starting a new game fixes the issue. The savegame file is too large to be uploaded to the forum, so here's a link to google drive:
https://drive.google.com/file/d/1uK81votGdXCbYjJRu6rqUWtyCAtGu-6i/view?usp=sharing
I've also created a few alternate zombies, to add a little variety to your local necromancer lair. The first is a fairly straightforward variation that uses the hunched over animation set Kingsal created for his beastmen. Unlike typical zombies, these are fast runners.