I have had an issue where random mobs would freeze and would be invincible, and if I reload the world they dissapear, for some reason a mod said it was a duplicate of this when it is pretty much different https://drive.google.com/drive/folders/1oXnpIGzObjI5fTv9flESoYh58kY2ykLX?usp=sharing
I have got this issue too on 1.14.60 spawned in a custom village
I am not sure how to reply to OcelotOnesie's comment on this being a duplicate, but dude I don't think it is. That is invisible active mobs and this is frozen invincible false entities