RMA has become a case of hardware musical chairs, where the same items seem to be circulated until some poor fool accepts a defective item. Have heard of people being given bad replacement after bad replacement, particularly with graphics cards. Replacements so bad that they often don't boot or graphical corruption is evident instantly. With monitors, Dell, I have had to go through 5-7 monitors until an acceptable replacement arrives. The rejected monitors are really bad too, splotches of colors on screen, bunches of lit pixels etc.
With this motherboard case I pretty much had them admit they did this. I called MSI and complained about the poor quality of the boards, and the tech told me that they never had this problem before. In fact, they had given the first X99S replacement (the one that had 2 bad RAM slots) to another RMA case, and hadn't gotten any complaints about it. I was dumbfounded. I asked him to confirm that he had given a known defective board, for which I had them on record accepting that the slots were bad, to another customer. He was silent for a few seconds, and then said "we... ah... we managed to fix it". Total BS! They had told me that since the slot problem was unfixable at their end, they would send me another, which was the even worse X99A.
Most likely, the poor schmuck that was handed the X99S, was either running two sticks and didn't check all the slots, or figured that two bad out of 8 was acceptable for him (it isn't for me).