After some painful fault finding I've discoverd one of the sticks of RAM in my son's PC has gone kaput, it's an 8GB stick of 2400mhz HyperX and when installed it will randomly blue screen. I don't think I've ever actually have a stick of RAM go bad before and there appears to be no obvious reason why it would have happened.
The worst part? He's somehow now ended up with my pair of 3000mhz sticks and I'm stuck with a 2400mhz single stick (OCd to 2666) on my Ryzen 2600x!
The things you do for your kids...