Pinebook Pro doesn't boot most of the time unless connected via USB-serial!

[nib0]

So, I had some time to experiment on Saturday.

Following @wdt 's suggestion that it was a bootloader issue, I decided to just nuke the bootloader on the eMMC since I wasn't interested in preserving my installation. I booted from the SD card using the serial cable and zero-ed out a GB in the mmcblk2 device. I afterwards created a new GPT disklabel using cfdisk.

Code:

dd if=/dev/zero of=/dev/mmcblk2 bs=1M count=1000
cfdisk /dev/mmcblk2

That solved the booting problem. The laptop was now booting every time from the SD card.

Happy with my progress, I flipped the debugging switch, screwed back the backplate and dd'ed my minimal manjaro from the SD to the eMMC, sure that it would work.

Wrong idea! Boot failed again and after trying a few times, did the whole thing again (took off the backplate, flipped the switch, ..., erased eMMC). The laptop can once again boot from the SD card. It can't reboot however, every time I try I get an orange power led and a blank screen.

So, that's where I am now. A few questions I have:

• When there is a problem with the bootloader installed on the eMMC, why does the laptop boot with the debugging cable plugged in and doesn't without?
  
• What is the correct way to install the manjaro version of u-boot to the eMMC?
  
• Why does reboot fail even though normal booting from SD works?
  

Thanks!