Just bumping this because I'm still having the issue, anyone got any ideas at all?

If I remember correctly Steam's Warband achievements won't work with mod, but I may be wrong.
As for POP's specific achievements - they should work if Warband's files were verified and mod freshly installed.
It shouldn't change anything, but you may try to disable cheats in Warband's splash menu.

I tried verifications, reinstalls, alternatives to steam workshop, everything under the sun and can't figure out why my PC in particular has zero pendor specific achievements. Normal warband ones work fine so it's mod related but something tells me it's on my end. Either way I kinda just chalked it up to a lost cause, worked fine on my old PC so I do wonder what's going on. Wish it gave me some degree of an error to work off of, but there really isn't even a trigger or anything to give me a clue.

I don't remember anyone reporting an issue similar to yours. Usually there is a problem with rewards for POP's achievements (when you get the "cheater achievement" you still get POP's ones, but without rewards).

There are two more things to try:
1. uninstall both Warband and POP, after that go to the Steam folder on your computer (location lilke ... \STEAM\steamapps\common ) and delete Warband folder, if present.
2. If you have access to the other PC with POP's working achievements, start your game there, save and transfer this save to your main machine.
If you don't have access let me know how you create your character, name, gender etc. I will do the starting save on my machine and share it with you.

Well I tried,

1. Deleting the warband folder from common, deleting the pendor folder from the workshop folder (one named with the weird numbers) then reinstalling via workshop

2. Same as 1 but reinstalling via moddb just to see if it was a steam issue.

3. Double checking if tweaks or enabling/disabling cheats did anything.

4. Restarted PC in between steps 1 and 2 just to be sure.

None of these seemed to work, honestly I'm plain confused but also kind of chalking it up as just piss poor luck on my end lol. I appreciate the assist but I might just continue to play without, isn't a huge huge deal to me but I'm hoping maybe some of the info here will at least assist anyone who may have a similar issue in the future.