Please try with a clean installation of the latest LE10 beta, leave config.txt and distroconfig.txt as they are and add the following options to the end of cmdline.txt:
video=HDMI-A-1:[email protected] drm.debug=0x04
This should give you working video output at 1280x720.
Then ssh in, run the following commands and post the URLs you got from them:
If video and audio are working fine you can then drop the drm.debug option and just keep the video option in cmdline.