I'm having a very odd issue when installing Ubuntu on my new system: once the LiveUSB hits the desktop, the computer abruptly reboots. Normally I'd consult the logs to see what happened, but it seems LiveUSB don't like to log things.

I've tried quite a few versions of Ubuntu (19.04, 18.04.3, 18.04.2, 19.10 daily for newest possible Kernel, Xubuntu 18.04.3 and Ubuntu Server 18.04 for a GUI less test). I've also tried quite a few options in the motherboards config, but to no avail.

Hardware is the following:
Annoyingly 
- Ryzen 3700X
- Gigabyte X570 I Aorus Pro Wifi (with latest microcode to fix rdrand issue)
- RX Vega 56 Graphics

Windows does work on this system, so it's *probably* not hardware failure.

No CPU/RAM/GPU overclocks; XMP for RAM is enabled, but I have tested with XMP disabled and it does not appear to make a difference.

Are there any ideas for what's going on here? And if not, is it possible to get log files from a Live USB?