I'm not exactly sure how to stop it from crashing, but to get your characters back, doing the follwoing should work:
1. Uninstall the Map Pack
2. Start up FeralHeart and choose any of your characters that were stuck
3. You should be in a blank, black area at this point. Click on the feather icon on the bottom right, and click it.
4. Teleport yourself back home and you should be good to go! :3
I haven't had any problems with the new map pack, but maybe after you uninstall, try to reinstall and maybe it'll fix? I'm not sure. It's just a suggestion, but best of luck~