Pahua's set crafting
Are you sure you have all the components necessary to change your ascended piece into a Trailblazer stat one? You’d need the gossamer insignia (which you craft after buying and learning the recipe), the armor piece, 5 ectos, and the hero point item you buy from Miyani.
Yes I checked it few times but I found that more people have the same issue…
Then yup, I’d personally consider it a bug. Hopefully it’s a bug that will be fixed at some point.