Starting from scratch:
Using Etcher select and burn your:
"openwrt-18.06.2-mvebu-cortexa53-globalscale-espressobin-ext4-sdcard.img.gz" image without unzipping it to your SD card.
Reset your ESPRESSOBin to defaults.
Install SD card.
Boot and interrupt autoboot.
Set the following u-boot param:
setenv bootcmd 'load mmc 0:1 0x4d00000 boot.scr; source 0x4d00000'
Then save with:
saveenv
Then reboot and it should work. This will not work IF you use a utility to expand the filesystem.
Hope this helps.