Angry endermen (and through the use of commands, other mobs with the AngryAt tag / entity data) will move towards to coordinates of the targeted player, even if the targeted player is in another dimension.

This only happens with players; it does not happen if the targeted entity is a mob.

Steps to Reproduce:

This is easiest tested/replicated with two players.

Player 1:

1. Set the time to night. I'm not fully sure if it matters, but I did my tests at midnight.
2. Summon an enderman. Rename it if you wish to reduce the chance of it despawning.
3. Stand on an elevated platform above the enderman that has a Nether portal. Ten blocks or so is an adequate height.
4. Enter survival mode, if you're not already.
5. Anger the enderman by staring at its face.
6. Enter the Nether portal.
7. Move around in the Nether. Being on the Nether roof is best for ease of movement and low risk of taking damage or dying.

Player 2:

1. Observe the enderman, watching as it moves (in the Overworld) to the coordinates of Player 1 (who is in the Nether).

Observed Results:

The enderman will move to the same coordinates as the player who is in the Nether, but it will remain in the Overworld.

Expected Results:

Should the target change dimensions, I'd expect one of the following to happen, ordered from most expected to least expected:

Option A: Enderman loses aggression. Should the targeted player re-enter the Overworld, the enderman would re-engage in hostilities, provided that the enderman:

• hasn't started targeting a different player or mob;
• its AngerTime timer has not been reduced to zero;
• and the player is still within the enderman's detection range and LOS.

Option B: Enderman attempts to move to the last known Overworld position of the target. Upon arriving or failing to arrive, it would either lose aggression, or enter the Nether by happenstance and continue its hunt.

Option C: Enderman teleports directly to the Nether unassisted, to continue chasing the target.

Option A is the most expected result, or the one I'd consider most likely to be the intended behavior. When comparing option one to a mob the enderman is hostile towards, we can see that that's exactly what happens — if the enderman is angry at a mob, such as naturally at an endermite or another mob using commands, then we can see that the enderman loses aggression once the other mob enters the Nether.

Screenshots/Videos:

Enderman tracking player, Nether POV — The POV is of the targeted player. The enderman's coordinates are automatically updated in the scoreboard, allowing you to watch the enderman's position change as the player moves around.

Enderman tracking player, Overworld POV — The POV is of the player who remains in the Overworld. You can watch the enderman run around to different points for seemingly no reason.

Notes:

I have only tested this with an enderman in the Overworld chasing a player in Nether. I assume, but have not confirmed, that this also occurs when the dimensions are swapped, or when replacing one dimension with the End. I also tested with the time set to midnight.

I assume this happens because endermen seem to track the targeted player (but not mobs) no matter what, so long as the player is online and the enderman is within loaded chunks. Unlike other mobs, endermen are not deterred by extreme distance, obstructions, or broken line of sight.

I'm unsure if this is an intended feature, or if it should be considered a separate but related issue; please know that I am not using this issue to report that behavior as a bug, but just bringing it up in case it is relevant.

The primary issue can be recreated using commands with other mobs that have the AngryAt tag/entity data. For example, by bringing Player 1 (survival) to an obscured or blocked-off location, summoning a zombified piglin a moderate distance away, then having Player 2 (creative) run the following command:

/data modify entity @n[type=!player] AngryAt set from entity @n[type=player,distance=1..] UUID

then have Player 1 enter the Nether before the zombified piglin can reach or see Player 1, then the zombified piglin will continue following Player 1's coordinates despite them being in the Nether.

This issue is also very similar to MC-274007, an issue causing tridents with loyalty to ignore the dimension and attempt to return to the player's coordinates.