Update.
First of all, thank you to everyone that chipped in

That was nice of you!
I
think it's fixed

After messing around with XYZ, the TLDR is, I just wasn't trusting with it, so I did a clean reformat, and also chose to reflash the BIOS, to the existing one (as that's all there is) - now it was a BETA BIOS, due to the aforementioned security fixes, so I have to keep it on that.
XMP enabled, everything is setup how it was, bulletproof - the BIOS in the past has decided to be strange when I keep fiddling with it (I had recently changed my PWM %'s a few times tweaking the noise/temps), so I think it was just throwing a tantrum

I don't think it was a hardware issue with the cabling, but I did reseat everything multiple times, and managed to tidy up the cables and route them a bit better - so at least I got something out of it
Thank you again so your help, I'm glad that my ram wasn't duff, and nothing needed replacing - considering it's all brand new bar the ram, which I'd tested many times and again when this occurred. Nothing beats fixing something for free
