Zombie ghosted through wall to kill me

I was AFK in my zombie farm for only about 10 minutes but when i came back i was long dead and all my things had disappeared except the armor and sword which the zombie picked up. I was in a completely sealed room which was well lit and the zombies cannot escape  the farm I am sure of it, I have used this design many times before on different worlds and have never had this problem. I am not using any mods at all.

Edit: the farm works with pistons pushing a trident on the floor to damage the zombies, the zombies were pushed out of the walls around it by the pistons or by entity cramming, either way this  is a new issue as i have used this farm design previously multiple times.