rockpro64 cannot boot from externally powered usb-to-sata interface

[working-name]

I flashed a 500gb 2.5" hard drive that's connected to an externally powered usb 3.0 to sata adapter (seagate). Using buster-minimal-rockpro64-0.9.14-1159-arm64.img. I also have u-boot installed, latest release, flashed from the same buster image.

Anyways, I can boot the image above from any usb thumbdrive on any usb port. When I try to connect the usb-sata interface, nothing happens - screen stays off the whole time. I already don't expect anything on the screen with u-boot - I'm guessing a UI is not a thing for that - but when I boot a usb 3.0 thumbdrive display comes on as soon as the kernel loads.

I can hear the hard drive spin up and move its head a couple times in the beginning but that's where it stops. Since I can't see anything on the screen, there's no errors, how do you even begin to figure out what is going on?