Hi,
Boy oh boy what a frustrating experience these amlogic boxes can be. I've spent days and days reading all 90 or so pages of this topic, endlessly going back to some section or other to check back on newly gleaned nuggets of information, tried countless ways of getting all sorts of images of Librelec flashed on what I believe is an S802 MX III 1G/8G box from around 2014, to no avail, and only to end up bricking it.
The main problem I never really got past was the file corruption error at boot time on the sd card. A usb attempt booted the Librelec install at the early stages when I still had an older Android image, but then got into a boot looop. Recovery mode seems sometimes reachable, sometimes not. Later I got the Remix image flashed and working (which also installed a working TWRP recovery) but it didn't help booting librelec from an sd card, and neither did any of the other fixes suggested (flashing 812 bootloader or image containing one, flashing dual boot fix, adding a nocompat file...). When I tried bypassing the sd card file corruption problem by flashing even earlier or different flavours of Librelec some got past boot but none ever managed to complete an install, freezing up instead or crashing with storage or memory errors.
What's hard to comprehend is the variable behaviour of this box: sometimes one method will seem to work, then later it no longer works...very tough to proceed in a pragmatic way when the parameters keep shifting on you. I'm not sure who the manufacturer of my MX III is, I got it on Amazon and the two names mentioned in the original ad for it ("Andoer" and "Dodocool") seem at best to be very minor players so maybe I have some sub-standard clone. Under Android 4.4.x the box worked ok though but using that it seems tough to get a recent version of Kodi working properly.
Anyway, to give merit where it's due, for the record I also have a Raspberry PI 1 B+ from around the same period, and I was able to flash Librelec 9.0.2 on it at the first try and it brought up Kodi 18.2 fine. The user experience is a bit sluggish for everyday use but it can run a 1080p video if you're patient enough for it to load up. What's annoying is I reckon the MX III hardware would probably do better than the PI...if only I had managed to get the pesky thing to make friends with Librelec.
I guess I should just bite the bullet and buy the most up to date box for which an official Librelec image is available. Thanks to all those who contribute here and elsewhere for the ride.