Not enough power from USB3?

I’m having massive problems powering my RAK5010 by USB3… Very often it goes into a continous reboot cycle (both led’s off, blinking a few times, off again). I’ve read multiple places I should use external power - but I’m uncertain if it’s OK to use USB connection while using external power - two power sources, is that OK? And it surprices me 900mA @ 5V is not sufficient for RAK5010?

Firmware Version: RUI v3.0.0.10