The game sometimes fails to credit both professions when a character has 525+ in two professions.
Tailoring/Enchanting credits properly
Blacksmithing/Alchemy does not credit properly (alch credits)
Skinning/Herbalism does not credit properly (skinning credits).
Characters in question have the requisite rep (or more).
This achievement gates heirloom pants and having sunk tens of thousands of gold and many hours leveling obsolete expansion professions in pursuit of it this bug is worth fixing. I see old bugs referencing this except when there was a higher threshold so the achievement was changed without being fixed.