This is a duplicate issue to MCPE-182594. After taking damage, the health bar in the HUD does not fully regenerate and displays half a heart less than the player's actual health. As a result, when a player has half a heart of health remaining, the HUD incorrectly shows 0 hearts. However, if the player takes damage that would reduce their health to 0, they die as intended.
This has also occurred in Seed: -8465638993189834603 on Bedrock (Xbox). Coordinates: 161, -13, 85
Flooded area enclosed within the trial chamber spawning both drowned and glow squid with no spawner.
Edit: A creeper also spawned around the water fountain within the chamber Coordinates: 131, -20, 77