with my mods and running on 1.12.2.
located outside a cave, only one of the droppers (kind of) works. only a bit of XP works, if someone could fix the mod, that would be amazing, thanks!
What's your intended goal with the mob grinder/farm? I've taken a look and the mods I've never used before but I am familiar with the names and concepts so I thought I'd take a look at the world and what you have set up.
The spikes obviously defeat the mob, but the highest between the conveyor and the spikes does defeat the mobs and not resulting in much XP by the looks of things, the hopper can send xp (in fluid form) or items to inventories like a chest or tank. The Hopper seemed similar to the one in OpenBlocks which is a vacuum but can send items/fluids to inventories if you want an idea of how it works in video form I'd say look up openblocks vacuum hopper or a Mob Grinding Utils mod spotlight. But that's what the hopper is supposed to do is collect and transport to the next inventory (or if you have a hopper/other pipe from another mod use them to transport).
As far as I can tell I assume your struggling to work out where the XP orbs or the rotten flesh goes with the zombies? I did struggle to work it out a bit as it's not the same block space it seems, just within the 2x2 space you have setup but I'd say just have 1 hopper collect the items and xp orbs (put into the tank in fluid form) and have a chest on 1 side with the tank and fluid targeting on the other but still a 2x2 of spikes and see if that works. I'll have screenshots of my basic setup below.
The first screenshot is of the area the hopper can collect from and the other 3 screenshots just show what I was considering and the direction things would be sending/the settings I put.
I hope that helps. Please explain more though so I can assist/get a better idea of what your mob grinder goal is but I just speculated based on what it looked like and what I know of the blocks from other mods that do similar.