Using USB power of any kind is potentially a flaw in your approach, but the display plus WiFi is probably pushing the limits of the onboard regulators anyhow. Can you try the same process without the display? That’s a good way to show that it’s not the scan alone that’s causing this. To be sure, I’d flash the onboard LED several times quickly at startup, and then slow the flash rate down… then you’ll see that the board resets because the flashing will go back to the fast scenario briefly.
Also, not sure I know which board you’re using, can you add that to this thread so there’ a relevant track of it?
Onto USB. USB is limited, by design, to the amount of power a device can draw. If a USB powerpack decided it was only going to work in scenarios with low-power devices, it may not power your device properly. If you have a high-power phone charger that has a USB socket, I’d try that as most of those can deliver at least 1000mA which may keep you out of the danger zone