Sometimes when exiting a boat, and then immediately trying to sit back down in the driver seat, the player can enter a broken state where you cannot open the inventory, cannot equip items via hotbar, cannot attack, and the in-world HUD that shows actions such as "Get in [HOLD]" will disappear.
After jumping the HUD re-appears and I could attack again, but the inventory and hotbar remain broken. Holding F to try and sit down again doesn't work and just causes the in-world HUD to disappear once more.
I'm assuming that this issue is caused by trying to sit down at the exact same moment the game attempts to teleport the player as seen in this ticket, as the timing seems to line up very well. Edit: Read additional info section
It seems like the only way to fix the issue is for the player to relog.