Hi, What kind of monitor did you use for RPi4 setup, and what is the max. supported resolution? The 720p resolution is something standard for TV's. Something very strange happening with your RPi4 setup. Could be the HDMI cable, was few cases with poor quality HDMI cables what isn't supported higher resolutions (the monitor resolution?). Or the power source, I had something similar with my RPi3, when I connected something to RPi, after reboot wasn't had picture. Or TV EDID detection, could you try with another TV? Or after fresh TV setup, when the screen setup is done, try to send thru SSH the "getedid create" command. That will save the TV display parameters (EDID data) and will use it at every startup.
The monitor is from AOC and max resolution is 1920 x 1080. The same type of cable is connecting another rpi4 to the monitor, but of course that does not mean that the cable used for the libreelec pi is not having a defect. I have ordered an adapter now, so that I can use a normal HDMI cable with the pi. Lets see how that goes. I have no other tvs to try on, but hopefully its all about the cable. I will get back when I have some news.
