It's or voltage or temps issue. When I see how my 7700K is acting I can only say that air cooler or something like 240mm AIO is not enough for 1.35V and in most cases not enough for 1.3V+ at full load.
@trents, I don't think this chip requires so high voltage,
it should run at 1.20-1.25V at 4.8GHz or something near. Play with LLC settings and maybe vrm frequency if you have these settings. Too high voltage is causing instability ( because of temp spikes ) and 1.35V can be already too high.
Other thing is that maybe you have a hot chip. My 7700K runs at high temps and I'm thinking to delid it this week and test which TIM is the best ( so far Gelid Extreme gives be the best results ).
I still laugh at MSI and their 5.2GHz 1.5V OC profile for AIO water cooling

I had to run my 7700K on single stage to deliver low enough temps at 1.5V+. At 1.6V+ I already needed dry ice to see improvements.