Wandering Trader causing Boat Chest to despawn

So I wander back to my base and find a wandering trader randomly sitting inside my boat with chest in the sea. I think nothing of it and logout.

I log back in the next day, only to find that the boat with chest has completely vanished, along with the wandering trader and some of the goods I had stashed in the chest too.

I am lucky I didn't have diamonds stashed in that boat, only a goat horn (RIP).