I realised just after I posted this that you could use the scoreboard value like that, had a blonde moment.

@Tez1010 What I had found was that by setting the volume values test appropriately you can check whether the border has been passed.

I don't understand what you mean by this, would you mind elaborating a bit for stupid me.

I think the entity vanishing might actually be because the chunks it is in aren't loaded when I exit the game, so they don't get saved at any point after the entity is teleported there.

This is all very weird. I was able to tp an entity to an unloaded chunk (whether generated or not) and the @e selector seemed to be able to find it indefinitely. I could wait as long as I wanted to bring it back as long as the chunk it was in didn't get loaded loaded during that time. I also didn't have any problems running /execute at the entity for as long as I wanted.
Even stranger if I tpd myself to the entity it was there, but if I reloaded the world and then did the same it wasn't there (or anywhere in fact).

I also realised that getting the coordinates of a player as a scoreboard value isn't at all helpful for what you want, because you can't use scoreboard values as variables.

Nice, good to hear you're making progress!

@Tez1010 It may be that you cant set it beyond the default of 60million he refers to.

Yes sorry I meant you can't tp a mob outside the default +/- 30million border because the game won't let you tp to values that exceed +/- 30million. Even when using relative coordinates. I guess a border you set yourself works differently. I did also think this might make finding the coordinates of a player much easier.

@Tez1010 He also refers to an operation you cant do only when you are outside the border to test whether you are outside the border. I cant find this - only ones that always work or always don't.

I think this got fixed a while back, I couldn't get it to work either. Seems like any command you try to run using coordinates beyond +/- 30million fails now.

The fact that tping back and forth through unloaded chunks won't load them if you use a mob is really strange to me, but convenient for file sizes. Just bear in mind that if you use a player I'm pretty sure they will cause the chunks to generate (haven't tested it though).

Regarding the types of loaded chunks, not sure what you mean. Are you talking about the difference between entity-processing (or fully loaded) and non-entity processing (lazy chunks)? If it is I don't think that's something you need to worry about because commands like spreadplayers will load the chunk to be entity-processing. If you can tp to the entity it's in a entity-processing chunk.

If you're interested you can easily tell if a chunk is entity-processing or not by setting up two command blocks with /say in them. Attach one to a redstone clock, and attach the other to a detector rail with a minecart on a looped track. If the chunk is entity-processing both command blocks will work, if not only the redstone clock one will.

@Tez1010 I could tp to the entity for a similar time window as for the back command referred to earlier.

This time window is actually linked to the autosave. When the game autosaves every 45 seconds it also tries to unload all the chunks it can. This runs like a clock, so you'll actually find the period of time you're able to tp to the entity is variable depending on when in the clock cycle the chunk was last loaded.
If you want a visualisation of this Wout came up with an autosave detector a while back:
https://www.youtube.com/watch?v=oGzQzqtCNY0
It works because any artificially loaded chunk (e.g. with hoppers) will be unloaded for one tick as the game autosaves before the chunk loaded loads it again.

I need a rest after typing all that...

Just properly tried using commands for the first time!
I found some interesting things you might find useful:

Firstly the method in the video I showed is no longer possible because you don't seem to be able to teleport entities outside of the worldborder any more. I'm pretty sure you can still find coordinates using something similar to this by testing if a series of relative tp commands succeed/fail, since they will fail if they try to tp an entity outside the worldborder.

Secondly you can tp a mob around unloaded and ungenerated chunks just fine. I only tested this by tping it out once and then back. There might be a limit on how many times you can tp it around unloaded chunks before the game can't find it any more. Strangely, I checked using MCedit and found that this doesn't load or generate the chunk (so no memory problems!).

No idea if this is remotely useful or not, but I had fun playing with it!

@JKELLER4000 it shows mobs in the stairs!
I tried reading through it to find why this might occur.

@NutjobBob it's this bug

Seems like no-one actually read anything I posted...

To spell it out:

@JKELLER4000 so it may miss that the mobs need to be spawned with enough room. and spawn them in places with only one height.

This is kind of right - the spawning for sieges doesn't do all the normal spawning checks and can lead to zombies spawning inside some blocks. That's all there is to it.

@JKELLER4000 i know if i warp. sometimes i get stuck in the block below me. so maybe there was an error, when you logged out or logged in that caused the mobs to be in the block below themselves. similar to when i warp sometimes.

This is a totally unrelated thing which I think is caused by a desync between the server and your computer.

As I said above, the fix is simple. Have less than 10 doors in your villager breeder and a zombie siege can't happen.

@JKELLER4000 right now we have render distance of 6?

I don't know where this rumour keeps coming from. It's still 5, and you can test it very easily in game using redstone or entities.

Also your maths is a bit off - you've calculated how much of a circle with radius 128 can be filled up by a square with a side length of 96. What you actually need to do is calculate how much of a square with a side length of 112 is no inside a circle with radius 128. Which is 0%

Why is the square side length 112? Minecraft only processes entities like mobs if they're inside chunks that have at least a 5x5 area of chunks loaded around them (i.e. 2 chunks out in every direction). This means that although the render distance is 5, entities only get processed up to 3 chunks away from the player. Which makes a 7x7 chunk square around a player that processes entities (counting the chunk you're in).

Mr Pythagoras makes it easy to see entities never get to beyond 128 blocks from a player:
approx furthest away from player entities can be processed = √(64^2+64^2) = 90 ish blocks

@CraftyMyner When there are only 10-20 players, mob rates are about 100%

I'm really surprised by this (I also don't really understand what you mean or how you got this number) because any player standing still or not moving around much will accumulate mobs around them over time that can't despawn, but fill up the mob cap. I guess with so few players on people don't afk enough for this to matter.

@CreeperLord170 did you actually bother to read the bug report?

@NutjobBob I vaguely remember seeing a video a while back

Found it!

Click!

I can't help but think there must be a better way to do this, but this method is pretty neat! (assuming it still works). Skip to 2:40 to see the bit about finding the coords of players.

Edit:

@Tez1010 upstaged by the area effect cloud

Hey thats pretty cool! Didn't realise they could be use like that. I assume you can't name them like armour stands though, hence the trouble with making them distinct.

If you reduce the number of doors to less than 10 zombie sieges can't occur. You can make a villager breeder with only 6 doors so that shouldn't be a problem.

By the way a villager breeder is counted as a village by the game.

@javonjw not near a village but i have like 15 villigers

Do you have any wooden doors nearby that the villagers might see as a village?

I suspect it's this bug , especially since they're all zombies. In which case the easiest fix would be to remove any wooden doors nearby that might be making a village (assuming there are any). Alternatively try swapping your floor for slabs with a block space under them.

If it is this bug the spawns should be quite rare since zombie sieges only have a 10% chance to happen around midnight if a player is nearby.