It appears there is some drama over PolyMC (if you’re using it). The M$ key they use has been revoked, so you can’t even login if you are using it. Don’t update PolyMC, upstream appears compromised.
The pack should be playable with MultiMC, and I’ll test that soon. If you do switch, make sure to grab your Journeymap data, NEI bookmarks, and options.