Everytime i join a friends game it would crash him.

Every time I join my friends world New beginnings it would crash him. This happened lately when we were starting a big project on making a bridge. I can never join him again and for hours we tried to find ways to fix it but nothing worked. Re-installed export worlds and what now. After many tries we just wanted to see if we can still join each other. So I created a world and he was able to join me. Okay good but when he made another world I joined him but It also worked. So I don't know what I happening I really want to build on his world again but it won't let me or him do it together because it keeps crashing him when I join him. It was like my character alone was corrupted or something and it wouldn't let him load me in that specific world.