Some servers restrict iron drops from iron golems to prevent the building of giant automated farms, or restrict any drops from environmentally-killed monsters, again, to prevent the creation of giant automated farms.
This might be done for gameplay reasons (no supplies of infinite free stuff) or for server lag reasons (no concentrations of hundreds or thousands of monsters collected in a tiny spot).
Docm's advice is about the distance between two villages.
Your target is to build one village and another one far enough from the first to be counted as another and not the same village.
As the distance of your villages is 75 and the minimal distance between villages needs to be at least radius+32 Blocks, while radius describes the distance between the first village's center and the furthest door of it, your villages shoul be far enough from another.
There are now two error sources:
Either you have got any door between these two "villages" which connects them to one large, or you are too standing too far away from the not-working platform.
In the first case, destroy the doors in the middle.
If you haven't got any doors in between these villages, just try to play/stand/run whatever between them.
Depending on the servers configuration there is a limit of blocks that may be between you and the mobs (usually about 60-80 blocks). If you are too far away the mobs chunk stops working. This means, the mobs are not running around, not spawning anything and for sure not breeding anymore.
So, to get your farm working properly, make sure that all chunks of the farm are loaded.
Which you may either achieve by being between them or putting one of your friends at he bottom spawn layer and yourself at the upper.
Depending on which plugins are installed on the Server there may be even a block or something called "chunk loader" but one of them at the bottom-spawn-area and your problem is solved.
Best Answer
Spawn chunks might work differently if there was no player there in a long time. The Minecraft wiki says:
If you can use operator commands on the server, you can use the
/forceload
command to keep the chunks loaded, when no players are near or are online. (More details here)If you have no operator rights, or you just don't want to use commands, you could try and build a machine that loads the chunks (e.g. the machine in this video), but this might not work.
And here's some additional info on chunk loading, if something's still wrong.