Armada 388 SoMs from older stock still ship with a very old version of u-boot which can not load from USB. Upgrade to v2018.01 or v2024.04 is recommended for general usability.
This document outlines how to upgrade the u-boot that is installed on eMMC.
Prebuilt binaries are available here, pick the file suffixed -emmc-boot0
, either:
u-boot-clearfog-base-emmc-boot0.kwb