If the server is under some load (approximately >100 entities in the Nether in my case, but that might differ for better systems), entities transported to the Nether from the Overworld (and maybe the other way around) can end up at a different portal than the one normally getting used.

In particular I have 7 portals.

Overworld: (3x3) centered around x=353 y=146 z=592 (my safe spot) and 4 (3x3) portals centered around x=353 y=37 z=591 (cube formation, part of a farm pushing mobs into them - to provide some context). Y levels indicate the bottom obsidian block.

Nether: (2x3) at x=44/45 y=118 z=73 and (15x3) centered around x=44 y=71 z=71 (the mob cage).

Distances: safe spot to high nether = 28, safe spot to low nether = 69, farm portals to high nether = 81, farm portals to low nether = 34.

The high y level safe spot portal will at times with heavy load (and never when "idle") occasionally transport entities to the lower portal in the nether which to my knowledge should never happen (closest portal should be the target). This happens for mobs (phantoms in my case) and the player (which lead to me getting stuck in my own farm and dying to hundreds of drowned - hilarious <3). Additionally, mobs from the bottom overworld portal can also be transported to the top nether portal (drowned in my case).

Now this is obviously not a terrible game breaking bug, but it'd be nice to see this fixed.

I'd be interest in just an explanation for now either way (is there some kind of optimization going on for when the server is under load?). Thanks!

Here's the link to my test world (sorry that it's so big, it's just our regular SMP): https://drive.google.com/open?id=1J7tV8hxS5kaZq1Fnhb5j8Fkqn8MI_Wzg