Loba "Loot legendary items" challenge not progressing..

I think it only works when you use Black Market to loot a gold (or it just works randomly idk)

Have you had any luck since posting? 

Did you try what I suggested worked for me where you have a gun equipped eg Havoc and then from the marketplace you loot gold mag/turbocharger etc? When I did this method I could see the challenge had updated in game.