Name the screen and session route
Write down whether the video is playing directly in the television application, in a computer browser or through a phone-controlled cast. These sessions can expose different places to inspect the next-video setting. The same signed-in Google account does not by itself establish identical player choices.
For a household that wants one selected documentary to finish without a related video following, check the screen used for that evening. An old note saying Autoplay off on laptop does not test the television. This is a local viewing preference question before it is an account-synchronisation fault.
Use the control for the current surface
The official help gives a player switch on mobile and computer, a settings route in the TV app and a queue/control-bar route while casting. Read the expected state after making the intended choice. Changing the phone’s ordinary watch-screen setting is not a substitute for inspecting an active cast’s controls.
YouTube also says scrolling past the player or typing a comment or search can prevent the next video from starting. If Autoplay appears not to work, record those interactions before concluding the switch is defective. A selected option and the conditions for its action are separate observations.
Keep age and inactivity rules in scope
The help identifies different defaults for younger users and the possibility of guardian-managed settings on supervised accounts. Do not bypass a guardian’s control merely to reproduce an adult tutorial. The page also describes stopping after inactivity under particular network conditions; that is not proof the preference changed permanently.
For an enquiry, report the device, direct-versus-cast route, visible switch state and what happened when the video ended. This evidence distinguishes a per-device preference from an interaction or supervision condition. No account or device setting was changed in this research, and no universal claim about how long every unattended session runs is made.
Questions about this guide
Does one Autoplay setting apply to every device?
No. YouTube explicitly allows different device settings.
Can casting have its own control route?
Yes. The help describes the cast queue/control bar on the connected mobile device.