I doubt this is the EEPROM configuration (e.g. BOOT_ORDER), my boot order is 0xf14. Then with an up-to-date Tumbleweeed on a USB disk (ssd or thumb), I get boot stopping before starting grub. Stops in u-boot input console. Following the bug Description I can replace bootfs:uboot.bin from LEAP15.5 and get Tumbleweed to boot as far as what looks like grub2 but there are no OS versions to boot.