I saw that there was a lot of people confused in the discussions, so I decided that I would try and help people not go through the pain I had to go through to get it to work

Put "keep corpses" on
Put "ai_serverragdolls 1" in the console
Disable all animation mods
Disable, and uninstall any ragdoll mods (You can save them for when you find the problem and download them)
Disable ALL reskins, even if they aren't related to the NPC you are trying to test (For me, this is what fixed the problem)
If none of these fixes work, disable ALL mods, and enable them page by page to try and narrow down the problem (This has helped me in the past)

After each of these, test it on both the normal metrocop and the combine soldier. It should look like the videos, the ragdolls holding the wounds and falling off buildings in panic. I've found this video to be a good reference
I will update as I find new fixes
I will try to help people in comments, but don't hold me to that
Can verify that it works with my 500+ mods
I've also found that it is sort of incompatible with other Fedhoria-esque mods, like Euphoria
If all else fails, try a different fedhoria mod like Euphoria , or get something else like Wreakhavoc , or this collection of ragdoll mods I have that you can try out
Some custom npcs just don't work no matter what, like this one