Hello, 

I've been having this issues since snapshot 20w21a, and its been persistent in snapshot pre-release 1 and 2.  the issue occurs whenever I'm exiting/dismounting from a boat, both arms of my character are no longer visible even when i scroll over the items in my hot bar they wont show up, i cant use them either.  it doesn't happen every time but it does happen often. as an example of how often, i was transporting a zombie villager via boat to my base, along the way i would have to leave the boat to eat to heal up as the zombie villager constantly hits you while you are in the boat together. every time I would exit, i would experience this bug, and the only way for me to fix it was to save and quit to return to the title and then re-enter the world. i had to do this about 10 times each time i would get off the boat until I finally got back to my base