Invisible zombies

I fell off a tower then died. A few zombies were there and picked up my stuff. Then I go back over to claim it and the zombies are invisible, no particles, no zombie, nothing. I start spam clicking to see if I can hit them, but nothing, I lost all of my netherite stuff, and an elytra from that. They were able to kill me so many times Please fix this problem it's really bad and irritating. I tried to put the version as 1.16.4, but it wouldn't show. It's probably me being stupid but idk.