I had issues booting GT-King Pro using the original Android factory firmwares as Beelink tweaked the u-boot environment to minimise the point in the boot sequence where u-boot waits for input (e.g. IIRC the power button on the Pro being pressed). This makes the boxes boot a little faster, but also makes them a pain in the rear as you need to press the button at exactly the right time (measured in ms) to invoke restore mode; then u-boot checks SD/USB media for images and finds LE and boots. The official response from their developers is "keep pressing the reset button during boot" and after a few attempts you'll get the timing right. More recent Beelink firmwares appear to be easier to interrupt and work with so I assume they increased the wait period a little. I forget which firmware I have installed now (as only booted it once or twice) but it was from ~October ish last year. It's a nice box once you get over the install hurdle
I was also able to get an earlier version to install, but don't remember which version......... But that has been awhile.