Hi dtech,
I have two M8S - one running Ubuntu Armbian & other Libreelec (balbes150) - both boots from USB flash drive using multiboot.
On 1st you clearly mentioned that for S812 tvbox, "S805 and S8X2 devices can only be booted from an SD card".
Means USB flash drive boot not possible with your image.
I tried your image from USB and do not boot from USB or SD card - because of Multiboot.
However, If I remove multiboot, by using your image on SD card & toothpick holding, it boots from SD card. Works good. I don'thave to use toothpick from 2nd boot. It boots from SD card.
I want to use your new docker support. My both M8S boxes, after few minutes (3 to 10 min.) randomly removed SD card on and off. Afterwards, I can not store or read from SD card. It's for any image not only yours. Even if I boot into Android, SD card removed message always comes. I have tried at least 10 different SD cards (good brand), same results.
Is it possible to make your image compatible to Multiboot?
If I use your image with first time toothpick, it does not boot balbes150 image or Ubuntu image.
Thanks in advanced.