An FC buddy had a similar issue and it wasn't just RNG, his quest bugged out and somehow the Atma quest's completion flag got activated even though he never actually completed the quest, apparently others had the same issue too. He had to make a GM report and just recently got it fixed and could finally start getting Atmas from FATEs, I'd say you could file a GM report and see if you have that bug since it seems like GMs can check that.