Whilst playing with my mum yesterday, we had an emergency at home and had to step away from the game. After coming back, we had both died. We raced to the spot we had both died (less than 5 minutes), but all our items had vanished, along with three boats (two of them being boats with chests). We both died in the water. Previously, when we had died in the water, our items stayed for up to 3 days (game time) of travelling back to the spot we had died in. These things take the joy out of playing the game, especially when had there been no real life situation, this wouldn't have occurred. Usually when this has happened, exiting and re-entering the game has solved this. It did not fix this situation. This world was created because of another bug that caused a previous save to not load at all.
Please fix this bug!
Thanks for making a report. Unfortunately, there is not enough information here to confirm a bug. We would need steps that can be used to reproduce the behavior.
Dropped items despawn after being loaded for exactly 5 minutes. The items are still loaded if you allow the game to stay on the death screen. When you travel back and forth they would not be loaded while you are far enough away.
Boats should not despawn, but if you were killed by a mob that shoots projectiles, such as a trident-throwing drowned, the boats may have been hit and killed too.