Before Libreelec 12 it always started up in 1080p but since libreelec 12 it starts in 2 of the 3 times on 1024x720. I have to reboot a few times to get it in 1080p.
This sounds like there is an issue by enabling DDC lines to read EDID. Not sure how this can be random. I guess I'll need to test it for myself, but not sure when.
I just added video=1920x1080@60 to the append line in extlinux.conf. I hope this will fix it.
That will help with video resolution, but you'll most likely lose HDMI audio.
In case this is the wrong way to do it, what's the correct way?
To fix kernel/DT issue 
getedid doesn't seem included in Libreelec for Allwinner.
no, but you can find edid blob in sysfs and use edid-decode to get readable text. In any case, 1024x768 resolution is indicative to failed EDID read.
hi there, dont know if this coud help, i coud swear its since v12... sometimes i had that same issue, is unsual to happend, just very little times, but when it happends is after rebboting machine (OPi3 LTS), screens stars with 1024x768 and 4:3 format, then i have to shut OPi down, turn TV off, then TV on, then boot OPi3 and back to"normal" resolution (1080p 16:9), however i always thought this was because of my very old TV set (about 16 years old).
regards.
