I loaded my 1.18 world into 1.19 only to find that my farms of various sorts (enderman, iron golem, etc...) were not working as they should be. I came to find out that the named mobs that were key to making the farms work were despawning. I opened a new world to see if this was still the case, sure enough, it was. The mobs would disapear regardless of named status or if items were held by such mobs. The mobs I tested included zombies and endermites, both used in the farms I have.