Hey, i'm on a rpi3 b 1.2 with a 32GB cruzer fit that's been known to work for others and a sandisk ultra 32gb micro sdhc. installing 6.3-release via miniroot works like a charm and then if i interrupt u-boot to setenv boot_targets usb0 mmc0 pxe dhcp and say saveenv it just repeats the error fsm 1, hsts 00000001 until i pull the plug. u-boot also doesn't find any storage devices in general and if i try to boot without saveenv (just setenv) it says Device 0 unknown and boots into the ramdisk again.
Cheers, schojo
