RPI 400 Ubuntu mate 20.04.1-desktop-arm64 , instant power down

I'm trying to install Ubuntu Mate 20.04.1 but my Raspberry Pi 400 keeps shutting down before it even boots. Raspbian and Ubuntu Mate 20.10 boot fine otherwise.

Any ideas? There's no signal on monitor and it seems to be powered off since no leds are powered on and can't even numlock/caps lock.