Have had plenty of adepts from expert Nether,sometimes multiple per run but have only got 1 master worked adept from all the runs I've done.
I think it may be tied to how many champions you kill as most runs have only been bronze and silver for me.
I must have done over 50 of those full as well as dozens more to just the first boss, and I have only gotten one, as well as only one from Court of Blades where I also must have done probably over 60-70 of these. I'm level 272 in the season pass/light level 2041 if that gives you any indication of how much I played this episode (or like over 400 hours). The regular adepts sadly don't feel special either if you ask me when they only come with one perk and not even the other origin trait.