UBPorts doesn't boot even after booting into recovery

[defekto]

The easiest thing to do is:

Install ubports image to an SDCard using etcher from here https://www.balena.io/etcher/
Then insert the SDCard into the phone and power on while holding the volume up and the power/sleep button.
After you get the awaiting command screen plug the phone in and flash the emmc using the ubports image.

Not sure what is wrong with your install, but it probably isn't worth the time to fix. Re-flashing is way easier.  My bet is the bootloader or partition is corrupt and needs to be reinstalled.  You could use a command like dd to grab the first 1024KB (if the partition type is GPT) or the first 512KB (if MBR - My device is mbr) from the freshly flashed SD and try writing it to the EMMC. to see if you can get past the boot issue. OR you can Try to mount the EMMC in linux and rebuild the boot config manually.  Not sure how to do that since I don't know what bootloader UBPorts is actually using.

Good idea, I will see what I can do when booting from the SD.