Mobs don't ever despawn, limiting spawns elsewhere

Many have noticed that mobs in Bedrock edition don't ever seem to despawn, even when being out of range of any players and thus should be in unloaded chunks. I noticed this with Zombie Villagers, which ordinarily would despawn when there are no players in range to keep them loaded. I played alone and travelled far away and even to the Nether and every time I came back I still had a bunch of zombie villagers trapped in a room.

We also noticed that the life in our oceans is completely void, no fish, squid or dolphins. Only the occasional drowned. I suspect the above bug to be the culprit.

Please ensure that mobs are properly removed from the game world when moved into unloaded chunks.