Not 100% if this is a bedrock thing or a dedicated server thing.

We have made a lab on a bedrock dedicated server, and our named mobs keep despawning. This includes a creeper, and none of them have access to sunlight.  They are in 2x2 cages with glass panes on one side. Also not 100% if they are on a chunk border or not, I have not quite tested that yet, but so far they have been despawning in an L shape, so it is possible that these are chunk borders.