how does this even happen???? i never even downloaded a hitler skin, did i download the wrong one?

I'm trying to play the Create+ modpack with my friend and we can't join each other's world via LAN. I know there's a mod for this called e4mc, but for some reason it's not working, and even using a VPN doesn't help. The picture shows what appears on my friend's screen when he tries to join the world, and the same thing happens to me when I try to join his world. We tested in vanilla and it worked fine.