I experienced this with the Iron farm that I've been working on. First, I had a Drowned which I just picked up from the ocean that I built the farm over. I gave it a leather hat, and it was fine for a while, then randomly despawned. I tried again, and no luck. This last time, I used a husk from a nearby desert, named it with a nametag, and went from there. It lasted a long while, but alas, it despawned. In all three instances, they despawned when I had the chunks loaded. They were all in a minecart going around the iron farm. Version: 1.15.2 Singleplayer w/Optifine Client.
I experienced this with the Iron farm that I've been working on. First, I had a Drowned which I just picked up from the ocean that I built the farm over. I gave it a leather hat, and it was fine for a while, then randomly despawned. I tried again, and no luck.
This last time, I used a husk from a nearby desert, named it with a nametag, and went from there. It lasted a long while, but alas, it despawned.
In all three instances, they despawned when I had the chunks loaded.
They were all in a minecart going around the iron farm.
Version: 1.15.2 Singleplayer w/Optifine Client.