I investigated the issue more by using /teleport to move the "soul" of the player. I managed to uncover a game-crashing bug if you teleport into the nether. I'm MinecraftssYT. The bug also occured on servers, and prevented me to join. The zombies are following my "soul" as I'm controlling the regular player, I was getting dealt damage and knockback, even in creative.
Advancement Made! Intentional Game Design