Nametagged hostile mobs in my world behave as expected, meaning they do not despawn. This has been tested on guardians, skeletons, Endermites, Silverfish, etc. However, nearly all creepers named with a nametag will despawn instantly when the chunk is unloaded by either entering the nether or moving far enough away in the overworld. I have tried waitng in the area for more than 5 minutes to see if maybe it was related to the time between naming and unloading the area, but no difference. Logging out and back has the same effect.

This is causing a serious issue with a charged creeper farm, where I capture a creeper that spawns in the area and nametag it. The mobs land on a pad two blocks down without taking damage. They are in a glass tube, so I know they're not taking any suffocation damage. I am covering them with a piece of string and placing carpet atop the hole for safety reasons.

If there is any further test I can do, or data I can provide, please let me know.