Snowman & Witches still attack so it isn't like NoAI, they just only attack if what they are trying to attack is in their normal follow range. As soon as what they are trying to attack is further away (but still in the custom follow range) they behave like they have NoAI.
Withers & Guardians seem to behave like in MC-102965
I tested it with the mobs on armorstands instead of NoGravity now. Still the same result. It doesn't seem like this bug happens because of NoGravity:1