I’ve been having this issue pretty much since the collections for the cultural armor were released. I’ve also already submitted 2 or 3 bug reports ingame that have yet to bear fruit. As you can see from the picture I have collected at least 22 human cultural armor items (these are all the lower tiers, I also have bits and pieces of higher tiers). However, as you can see from the second picture, I am only credited with having collected 15. Since the items are soulbound on purchase I technically shouldn’t have to do more than buy them, which I obviously have. It’s a little upsetting to be pumping gold into these achievements only to find that they fail in correctly following your progress.
As a side note. I have attempted to purchase new sets not 3 weeks ago in a new attempt to finally complete this achievement. The armor skins were unlocked and the items were soulbound to the character buying them but the achievement tracker did nothing. This is only the human cultural achievement tracker that I’ve noticed but I also haven’t purchased cultural armor lately for other races nor checked if the tracker upgrades properly or is even at the correct setting for me at the moment, but I will look into that ASAP.
I hope someone from ANet reads this and fixes it, it’s been over a year for me :/