Yes. That is exactly what I was going to say. For the sake of being honest I have to say that of course I can't tell you that THAT "is" the problem, because there's always a chance that it is not, but being completely truthful, I have seen so many systems have problems with those N1 and W1 units it's a good thing EVGA has had some exceptionally good units at the other end of the spectrum or they'd have been run out of PSU town long ago as a result of it.
For certain, with absolutely ZERO doubts about it, that PSU 100% does not belong in THAT system with that level of hardware, and should be replaced with something much better no matter whether it is the problem or not, and I rather believe there is every chance that it is because those unit are incredibly flaky when it comes to problems and performance. I've seen quite a few of those N1 and W1 units have issues even in mainstream desktops that aren't using anything more than a slot powered graphics card, much less one with a high end hardware.
There were reviews of the 430w and 600w version of that power supply on HardOCP, but they have recently closed down the site except for somebody seems to be maintaining the forum section over there but all of the reviews are gone. The results of that HEC platform used in those units was terrible. The 500w version did slightly better in JonnyGuru testing, but even that only scored an 8 out of 10 which, while not horrendous, was still pretty lousy and was likely a cherry picked golden sample sent to them by EVGA. Off the shelf units don't tend to do that well and are more in line with the results that were seen on the HardOCP reviews.
Short version, it's a low quality PSU shaped object, even if it's not necessarily a dumpster fire waiting to happen.
Also, with a PSU that is very questionable, it makes it really difficult to even try and find other problems because you have no idea whether what you are seeing is a result of the cheap power supply or an actual hardware issue.