Hello…. Nothing bugged for me on this quest at all while doing it. I got the Passably-Forged Credentials on heroic, swapped to mythic to start the hard mode, spoke to Fe’tajid and entered thru the guarded entrance peacefully, and after finishing off So’leah, got the achievements…. “Tazavesh, The Veiled Market” on Mythic… and… “Mythic: So’leah’s Gambit” but for some reason, did not get the achievement Fake It ‘Til You Make it with the mount. What gives?
EDIT: I went back and redid everything above on another character and I got the achievement. This is the only thing different I did….. after using the Passably-Forged Credentials, speaking to Fe’tajid and getting through the guarded entrance, I re-armed myself with my original neck armor without clicking on the forged credentials neck armor (which I did on the first character)…. which removes your disguise. So I still had the disguise on, while having a slightly better boost with my neck armor, if that makes sense. I suppose I could have just left on the forged credentials neck armor and left it at that. Oh well… just glad I got that done! I guess you need the disguise while fighting So’leah?