Read the TV's input indication
A television can leave the input showing a player because another HDMI-CEC action changes the selected source. Google documents automatic input switching when casting to a supported connected receiver; Sony documents related BRAVIA Sync controls. This is a possible control event, not a universal diagnosis for every black screen. Note the actual input label and what happened immediately beforehand.
If the TV changes from one named HDMI input to another, preserve that observation. A stream freezing on the same input, a brief output-mode transition and a source change are different events. The device whose picture disappeared may still be running, so do not assume it needs a factory reset.
A hypothetical household interruption
Suppose one person watches an authorised programme through a set-top box while another starts a cast to a connected receiver. The TV moves to the receiver's HDMI input. Returning through the TV's normal input selector may reveal that the original programme continued. Record whether it advanced, paused or restarted instead of assuming the result.
Check the exact devices and their documented CEC or input-control settings. Manufacturers use different names, and supported behaviour varies by model and connection chain. Do not switch off every control feature at once. A broad change can also remove useful power or volume integration that the household relies on.
Use a short nonessential session for a controlled repeat. Identify the action on the second device and the TV response. If a cast target was selected accidentally, verify and clarify receiver names before repeating. Testing with private content in an uncertain room is unnecessary.
Choose and verify an intentional arrangement
If automatic input switching is unwanted, consult the TV and receiver manuals for the relevant supported control. Record the original setting and the effect of one change. The right arrangement depends on whether the household wants casting to take over the screen automatically or requires a deliberate input selection.
Afterward, test the original viewing route and the other intended control tasks, including volume or power where affected. A useful report gives the starting input, triggering action, resulting input and original player's state. This assigns the problem to a reproducible control sequence without claiming that the programme provider interrupted the stream.
Questions answered
Does a programme disappearing always mean the player stopped?
No. Check whether the TV selected another input and observe the player's state when returning.
Should I disable all CEC features immediately?
Use the model's documented controls and change only the relevant behaviour deliberately, then check the other control tasks the household needs.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.