Sometimes when a player sneaks to get out of a boat, the player starts bugging. They can't do anything and it seems like the boat is still driving even though it isn't. This bug has been going around since 1.16 I guess, and my friends and I often have this issue while using our Nether Highway. The player can get out of this when destroying the boat (it will drop at the player's location) or when rejoining the game. You've already fixed this issue in the snapshot 19w34a, but the bug came back. (By the way, it isn't as bad as it was back then, the boat won't disappear, but it's still a remarkable issue.) I'll hope you'll fix that one too.