Swift enemies (spiders, endermen, small zombies, piglins, etc.) attack from out of the player's reach. The faster the MOB moves, the longer the attack distance will be.
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Most likely a duplicate of MCPE-179969 as the issue here is also described there.
I think the enemy MOB's attack range is shifted to the front of the main body. Slower enemy MOBs are less affected, but faster enemy MOBs have a much wider attack range and will be attacked before the player's attacks can reach them. The situation is even worse in multiplayer, where you can be attacked from 4-5 blocks away, and without a shield you can't do anything and get killed. There was no such problem until the previous version (1.15).