Somethings bugged with online

me and my friend have been trying to play together recently and every time i try to join him it kicks me to the menu screen and if i try again, or try to open my own world after trying to join him the game crashes. if i open the game from steam i can play on my own world fine but when my friend tries to join me it shows his little name and distance at the spawn location on the docks but hes invisible, i cant see, hear, or interact with him in any way, and it keeps his little name marker on the docks… HELP!!!

Have you or your friend ever been using mods?
Mods are not supported and can break the game or even your safegames and make the game incompatible playing with each others.