I had no time in the last week, but now I was able to look at some things.
I could not make screenshoots (no USB keyboard in the house), so resorted to low q photos with my phone.
Here are the supported resolutions on my TV with your image and DTB (Samsung 43NU7122):
Also, I have a problem, with LibreELEC on this device, since I got it: on my UHD TV, when I watch 1080p videos, everything is a bit zoomed in, like this. But when I watch 2160p videos, everything is normal. If durring playback, I change the resolution to 2160, in the menu, it fixes the video, and the UI, but the subtitles dissapear, until I change the resolution back to 1080. But then, the video and the UI get zoomed in again.
Here is the log: http://ix.io/1gna