Certain mobs can have difficulty inflicting recurring hits on non-moving or too-close players

Certain mobs, if too close to the player will try but fail to damage them. Of the mobs I tested, it was easiest to reproduce and most noticeable with the enderman.

Steps to Reproduce:

The outlined steps will be with an enderman as the example mob.

Pre-test setup:

1. To prevent accidental deaths, affect yourself with high levels of resistance or regeneration;

/effect @p resistance infinite 255 true

1. Set the time to night to reduce the frequency of the enderman's teleportation

2. Set your gamemode to survival

Replicating:

1. Summon an enderman

2. Aggravate the enderman, by staring at it or attacking it

3. Stand still and observe the results

Observed Results:

The enderman will rush to attack the player, usually getting at least one hit. After reaching the player, it will continue to run towards them or stand next to them without attacking. Should it keep moving, it may get additional hits, but it's inconsistent. Once it stops it usually will not damage the player again, so long as the player doesn't move, fight back, and as long as the enderman doesn't reposition itself by teleporting.

Should the enderman fail to deal damage for long enough, it will lose its aggression.

Expected Results:

The enderman should rush to attack the player, and deal damage at a consistent rate so long as it is close enough. Performing this experiment with a zombie instead shows how I expect it to act, dealing damage around once per second.

Notes:

This was tested on a superflat world. I don't know if having a different elevation as the attacker would affect it.

This can also be observed with a creaking, though I was unable to get it to fail to attack indefinitely.

I could also reproduce it with a wither skeleton by continually running into it and staying within it, though I could only delay recurring hits by an additional second at best. In this case, I used a command block to continually remove the wither effect from myself, to make it easier to tell why I took damage.

I also attempted to reproduce this with zombies, vindicators, silverfish, and spiders, but could not; their attacks worked as expected.