In Mystery heroes, sometimes the weapon variant (golden weapon or jade) is not applied. I do not believe it is character specific and it seems to be random. it seems to be a race condition when loading the character or something. I can get Zarya in the first part of the match without the variant and later with and vice versa.
The most interesting case is with Reaper; when he loads without the variant applied, when he reloads and drops his gun on the floor his new guns will always have the variant applied