ROCK64 bootlocks with 2 usb drives

[Trash_Can_Man]

Hi, I'm veeery happy with my ROCK64 overall and I managed to setup Nextcloud manually on it. It boots via the USB3 port. (Armbian-Stretch)
I ran into a error though, which is really ruining my day:

I wanted to set another USB Flashdrive as the cloud storage, connected on a USB2 port. It all works fine when I connect it after the ROCK64 booted.
BUT the ROCK64 woun't boot at all when a second USB drive is connected. It locks before a screen output, so I think this is not an Armbian problem.
I suspect the SPI bootloader gets confused when it can't boot from the USB2 drive and it will skip booting from the USB3 port?

What I figured out yet:
Bootdrive connected on USB3 port, Storage drive connected on a USB2 port --> bootlocks before screenoutput
Bootdrive connected to a USB2 port, Storage drive connected to the USB3 port --> it boots and works perfectly fine

Question:
Can I force the bootloader to only boot from USB3 and don't check the USB2 ports?

You need a bigger PSU, that one probably is not stable enough...

Jokes aside if you try several times it eventually boot? im using allmost the same setup but i use both drives thru a powered usb3 hub, its a workaround instead of a solution but maybe works for you too...