We have had an issues regarding boats several times when playing split screen on the Xbox edition. The game mode is peaceful survival.

When traveling together by boats and dismounting our boats they disappear.

We can see each other boats though so we have solved it by getting it to our inventory and dropping it to the other player. See attached video of visible vs invisible boats.

I can only find resolved issues regarding this. Such as:

MC-153899
MC-101247