Mobs freeze on screen but actually continue to move as invisable

I am new to Minecraft, 
I found the following issues. 

1, Cows and sheep would appear to be frozen, but grass gets eaten no where near the frozen animal
2, I have been attacked by monsters. I cant see them but I get killed in an open room. If I Sleep and go back, sometimes I find the zombie, or Spider or Skeleton there. 

Sometimes my daughter can see the monsters on her PS4 but I cant