Have been running 2x16GB Corsair Vengeance Pro on my Asus Z390-F with no problems for the last 5 months, been a great build so far. But with current work loads I've bought another of the same RAM. Problem is, I can only get 3 sticks to run - 48GB, doesn't matter which order they're in in terms of slots, it sees them no problem. When they all didn't run first time, I tried one at a time, when through the whole test and got up to 3 sticks working in either slots. Any ideas what could be preventing all 4 from working? Fairly sure I've ruled out a faulty slot or stick of RAM. Even tinkered with the MemOK switch, no luck either way.