There is something wrong with RNG, though it might be a Doff only issue (or was, as I do not have it happen now as often as it used to). If I had a dollar for the number of times I have mass failed or mass critted 4+ Doff assignments in a row (as in a straight line, not 4+ randomly out of 20 total), I might have enough to get all 3 versions of the NW account packs. In the cases of mass failures, I normally had like 1% to 4% chances of failures for each, so having 4 or more in a group of 20 is possible but 4+ in a row would not seem reasonable, especially since it was pretty much daily at one point (or several times a day when I was overdoffing).