Sometimes when enderman is hostile and is attacking us, randomly he stops being hostile and stops attacking.This happens when he teleports or when he is taking damage and sometimes you running from him some time he stops being hostile

Additional information provided by jirauser521040

Endermen in all dimensions regularly stop being hostile towards a player after being aggroed by the player. This can happen after a second or a few seconds. It should also be noted that this is related to endermen teleportation as it is when they teleport that they loose their aggression towards the player.

While most obvious in the nether (as you hit the endermen once and it is usually never seen again after it tps) it can be observed in other circonstances.

This makes collecting ender pearls especially tedious and painful as the endermen rarely remains aggored long enough at a player for the player to be able to kill it.

To reproduce

1. Create a flat world in creative mode
2. Give yourself netherite armour for protection, a stack of enchanted golden apples, and a stack of endermen spawn eggs.
3. Make sure you are wearing the armour and then switch the gamemode to survival.
4. Once in survival, eat an enchanted golden apple to not die from endermen attacks.
5. Now, spawn one endermen on the ground using the endermen egg.
6. Stare at the endermen to make it aggro towards you.
7. Hit the endermen with your fist to keep it from hitting you.
8. Continue to do this until the endermen teleports.
9. Turn and look around to see where the endermen has teleported to.
10. The endermen will either have unaggroed or if he is still aggro, repeat step 7 to 9 until he unaggroes from you. (This should not take long)
11. Observe that the endermen has unaggroed from the player.
12. Repeat process to see that it is not simply a one off occurrence.
13. Note that the endermen can seemingly unaggro from the player at any distance.

Observed results:
The endermen often unaggroes from the player after teleporting. This can happen at any distance from the player.

*Expected result: *
The endermen should not unaggro from the player moments after having been aggroed by a player and as long as it has not despawned from being outside the simulation distance.