I am having the same issue with my Roku and Sony TV. The menu and app UIs display correctly, but sound and video content do not work. The progress bar show that the content is playing, and the preview thumbnail shows up when skipping ahead.
Sony Bravia 1080p TV w/HDMI 1.4
Roku Express 4K+
Software V. 10.5.0 build 4187-CR
I have tried adjusting the output settings from 1080p to 720p and back again, with no change.