Robert Parker

I'm having the same issue.  In an effort to find a work around for mobs despawning (MCPE-21416: Mobs and Entities can despawn randomly) I was trying to use the command blocks to re-populate but the spawn event string is not working.  No matter what one I use it creates a random villager with a profession or a child or anything but the string you have added seems to be ignored.  Example of command used was /summon villager ~ ~ ~ minecraft:entity_born

This was done in Win 10 Minecraft.

This despawning is occurring more frequently on my realm.  I have had entire buildings of villagers with trades and leveled up disappear, named entities are disappearing as well for both villager and animals.  I have had rare items like skeleton horses disappear.  It also seems like the villagers have a hard time finding trades and can get locked into a trade while then stationing at another area.  A farmer keeps going to a mason stone or a cleric to a compost bin.  When they disappear it seems to upset the logic for the trade to the associated task and I have to go around and break all stations and then replace one at a time until the villagers are reset.  This break in the linkage between the villager and their job seems to occur after a despawning event.  Tried to stop using nether portals and it improved but happened again without nether travel.