When using a boat, randomly (more often than not) when leaving a bot, it will render at the STARTING point, where I boarded it. If that happens, I can just hit around where I left it and, if I hit the (now invisible) boat, it will (quite hilariously) come quickly from the starting point to the new position (thus it does not simply render on the correct place, but "moves" to the correct place). 

If I forget to check if the boat is there and don't remember the exact place I left it (thus it gets tedious to hit around until I get it), the only solution to get it to show again is to go far away (entity draw distance) and back, at which point it will be on the proper place.

Seems to happen only with boats, and only in multiplayer.