We know that atma drops have been low this weekend compared to the initial rate when we released the atma drops in the Premium Dungeon. We adjusted the drop rates a bit more than we needed to following a very busy week of atma drops.
This will be revised further: We will double the base rates tomorrow during maintenance and that should produce proper results for all those players who purchased premium. Currently, note, as a measure of compensation: All Drop Rates are now set to 300% until we make the change tomorrow.
As of 9/12/2016
Also see this table about the changes before and after the adjustment and the "final" adjustment during tomorrow's maintenance: