Phantom Illagers!

I'm working on an event on my Realm for some friends and I to play through down the line that includes some custom mobs spawning. This includes a few groups of illager mobs (pillager, vindicator, evoker, ravager, etc.) I'll spawn them in using a summon code (ex: /summon vindicator ~ ~ ~ {PersistenceRequired:1b,CustomName:'{"text":"Dumbledorf\'s Warrior"}',HandItems:[{id:"minecraft:diamond_axe",Count:1b,tag:{Enchantments:[{id:"minecraft:sharpness",lvl:5s}]}},{}],HandDropChances:[0.005F,0.085F]}), then move on and continue building. Later, when I return to play-test the build, I notice that a handful of the illagers turn completely invisible; their models vanish, their custom names do not appear, and they cannot be interacted with using physical attacks, and even the /kill command is useless.
However, they CAN be heard, and they do still have a hitbox that can be used to pinpoint their location using splash potions (though timed effects like Glowing have no effect on them, so you have to follow the sounds they make and spam splash potions in that direction until you hit them.) The only way I've found to kill these entities is by precisely hitting them using splash potions of instant damage until they die.
Overall, their AI seems intact. They still drop normal loot upon death, and their pathfinder is functioning normally, as they are able to move about the physical space around them despite having no visible form.
They just can't be seen or interacted with.

I can't determine if this is related to the core game or just Realms, as I have not tested for this bug in single-player. Furthermore, not all of the Illagers programmed become these "phantoms", as it feels almost random which ones turn this way and which ones don't.

If you have any questions, please don't hesitate to ask. I will do everything I can to help so as to resolve this issue in as swift and efficiently of a manner as possible.