Posted February 17, 2017
Now, especially when you're talking mixed pairs there's a bit less certainty - different clock speeds, slight delays across the different motherboard slots, even same brands but different "models" of RAM behaving differently voltage wise. These little things can add up.
Again, I'm not even positive this will fix your issue but it's the first thing that came to my mind. Disclaimer - I'm not sure if Memtest would have picked this up or not (so I apologize if memtest already "cleared" you for this!). But if you get bored and feel comfortable, I'd suggest cracking open your case and leaving only a perfectly matched pair of RAM (or a single stick) and see if that fixes your issue. Even if you go ahead and drop the full 32 GB back in, at least you'll know.
If you do leave a matched pair, maybe even look around on the internet / mobo / RAM homepage to find out the best two (or single slot if you don't have a matched pair) to leave the matched pair in. You might have to play a bit of "musical RAM slots" to get it running perfectly.