Did you ever get to the bottom of this @heretolearn ? I have the same problem but I'm running 3x Sapphire 280x. I believe the advice about VBE7 is the best - cards with older BIOS installed don't seem to have the same problems, as they run around 10C cooler than the same hardware with newer BIOS installed. Basically, any undervolt needs to come from the BIOS and not an application like trixx, or the cards throw a fit.
The other possibility is that the motherboard isn't delivering the right amount of power to the cards all of the time, MSI is not an expensive brand, they are a relatively young company in terms of their competition. I have been having the same issue as you, and my Asrock board is definitely a possible factor.
Does this ring true with anyone else lurking here?
I am. I also had an spark coming out from one GPU. The riser burned. Righ now I'm planning to change all the powered risers, since the molex once in a while disconnects by itself.
I tried to direct connect he molex but the rig continues to shutdown. I believe that is the molex that isn't passing any power.
About the GPU despite the spark nothing changes. Everything seems to be working ok.
Running 4x Sapphire 280x @ 1090mhz engine, 1.175v bios