Firstly i will answer the first problem referring to Kodi Application in Android.
You are not able to set resolution in the Kodi Application because the crap Chinese Android OS does not have the correct permissions set to change resolution or adjust display refresh rate. Whatever you do in Android settings will not be used in the Kodi Application.
The result is Rubbish Playback.The second issue of Greyed Out Resolution in settings using LibreELEC is something i have only seen whilst using some skins outside of Confluence. Have you tried using Confluence when setting the resolution ???
I hope you haven't backed up an Android build and then restored it to LibreELEC as this may have caused it.Do a hard reset and then try to set resolution whilst using confluence.
That is all i can advise for now.
I haven't used the crappy Android version of Kodi.
When in the Android settings (not kodi android) i can change the resolution settings and that is what is used in libreelec, even if i run from nand. Also it's greyed out at the same time.
I am using stock Confluence.
What exactly do you mean by hard reset?