When your render is lower than your simulation, mobs can attack you from out of render, this is a big issue when playing at 4 chunks render or lower, since they lowest you can set simulation distance is to 5 chunks

Steps to replicate:

Set your render distance to a value between 2 and 4 (better results if using 2)

Set your simulation distance to the minimum possible (5 chunks)

Type /summon minecraft:ghast ~ ~ ~64

Stand still and watch how ghasts can attack you