Geoffrey Cly

this isnt a bug, the mechanics are designed to do that. I dont know the math but when you make a new portal in the nether and the multiply x*8 y*1 and z*8 then it will go to that exact (or closest) in the normal world

have you tried to remove the item frame and reset your .bin folder?

This has happened to me, it is more of a problem with slimes though. I think mojang messed up the hitboxes on big slimes during an update because now they are merely impossible to hit