I've been toying with this on an XU4 and have a couple of issues.
1. Firstly, out of curiosity, what is the difference between the builds? RetroELEC-OdroidXU3.arm-9.2-devel-20200312212432.img.gz didn't work for me at all (wouldn't boot, not output from HDMI port), though RetroELEC-OdroidXU3.arm-9.2-devel-20200309122419-251e0c5.img.gz works fine.
2. More importantly, AutoFS doesn't seem to be working, as the /auto directory doesn't seem to exist! I got round this but manually mounting my NFS share, though I can't seem to edit /etc/fstab to add it permanently.
3. On a similar note, I can't modify the emulationstation settings - when I open es_systems.cfg in nano, it says at the bottom [ File '/storage/.config/emulationstation/es_systems.cfg' is unwritable ]. I was under the impression that everything within /storage is not read only?
Any help would be appreciated! 