I know this is probably a stupid question and I apologize if this is a known bug or something, but how does one trigger the wardrobe layer achievements? I'm fairly certain the counts should at least be going up as I'm adding things because it's been awhile since I removed anything, but even the 'filled wardrobe' count isn't going up either.

Go to the items tab and select the individual layer from the dropdown. At least that's been working for me.

Pretty sure it's also a cache issue. You just have to go to your wardrobe, maybe refresh a few times then go back to Subeta's home page or any page and it should update. If it doesn't, wait a little bit and try again.

Seems like that did the trick, thank you!

No problem, glad it worked for you!