1 of the components on the PCB is getting slightly hotter than usual but there's not a huge amount of heat coming from it and this is likely because one of the chips draws more current every time it resets.

I know it's not impossible to get voltage that high with all the coils and capacitors in this thing but I find it hard to believe it would happen without being specifically designed to do that.

I've tested it several times and my multimeter was showing almost 2KV last night. Could there be some capacitance or something that's confusing the multimeter?
The main PCB has 4 large capacitors between GND and 12V. I've tried the multimeter in DC and AC mode. AC mode shows 0V between ground points.

In the PSU the secondary is *almost* completely isolated from the primary.
After the 240V AC is rectified, the negative goes through what looks like a very large blue ceramic disc capacitor to the negative on the secondary. Could this be causing issues as it's essentially linking half cycles from live and neutral to my PCB ground.

The problem is also strangely intermittent. It doesn't seem to happen for the first few minutes after being powered up. My PCBs work fine and the multimeter reads 0V between all ground points. After a few minutes it goes back into that state.

While in that state, if I put my multimeter between the 0V and 12V outputs on the PSU it reads 12V and my PCB starts working as normal. As soon as I disconnect it the PCBs start resetting again.

I've had the same PCBs running overnight using another PSU of the same type and it hasn't reset once.