Our old save uses these mods: 20% more difficult (or whatever it's called), MonsterScaling, Party Expansion, and the Void Knight Class.
Since the patch, when we try to connect to him we all go through an extra "installing" screen that lasted an hour. It was downloading a Patch6.pak file, which is 611 MB. Only two people loaded in, and the other person crashed and had to redownload it all over again. It actually just overrides the 611 MB file and just decides to start "installing" again.
It doesn't seem to be a problem if anyone but the host causing the problem plays. I could connect to anyone, and I could also connect to any other person from the group.
I literally can't find anything about this online, so I have no idea what's wrong.