When you experience reboot problem do you hear like someone turn off PSU on switch button and no power on motherboard for moment and than power back and PC boot or instantly only restart and power is all the time on motherboard.
Power never drops. When it POSTs the motherboard indicator light goes from red to green, but when it doesn't POST those lights never light up.
If there are no indicator lamps lit at all when it doesn't POST, that suggests to me a power supply problem. Maybe there is an intermittent power cable. I would try re-seating all power cables to the motherboard, including the I/O panel cables. Next you could try to test the power supply or replace with a known good one.
The bottom most indicator lamp and the RGB light both stay lit. Something may be seated incorrectly, but I doubt it's a psu problem because the previous psu worked fine with the previous build. I didn't start having issues until I switched platforms and OS.