A supported display-format switch can cause a short blank screen; repeated blackouts during steady playback need a separate investigation.
Why this happens
Some streaming devices change their output to match the dynamic range or frame rate of the programme. The television may take a moment to accept that new format, so the transition can include a brief black screen or flicker. That is different from a source that loads and then repeatedly loses its picture. Timing is the clue: does the blank screen happen once as playback starts, or return unpredictably while the programme is already playing?
Write down the transition before changing anything. Apple documents this behavior for its Match Content settings, but the same menu names should not be assumed on other devices. If blackouts recur, compare the affected format, HDMI input and connected receiver or soundbar through their supported setup instructions. Keep the ordinary menu display and an SDR item as useful baselines. Do not repeatedly reset the account for a display-handshake symptom; a login change does not explain why the television loses a video format that was already playing.
A useful way to work through it
Note whether the blank screen appears only when entering or leaving playback.
Review the streaming device’s documented content-matching behavior.
For recurring loss, compare one supported display/HDMI condition while keeping the account unchanged.