U-Boot Troubleshooting for USB Booting on Rpi 3B+ w/ Aarch64

[LucianoArm]

HI,
I habe followed the instructions from the installation page
(with Aarch64 image). But I can't boot my Rpi from USB. How kann I troubleshoot this?
I habe successfully boot Debian from USB.
Any hints? I have even change the Fstab file.

Thanks,