As such I won't search but summarize. It's usually the connection from boards to LCD or (bad news) the tab bond is failing. It's not a setting, input issue but hardware. As noted, some connection, plug or board issue. If it's the tab bond there are YouTubes on that but only band aid possible fixes since no one can repair tab bonds in the field.
Sometimes a thin vertical line shows on our TV screen a few centimetres in from the right-hand edge.
It's not there on all programmes although when it's there it will be present for the duration of a programme. Inputs to the TV are a Humax HDR-1100S (satellite), an Amazon Firestick and an AppleTV (Mk III) and each of these have been connected to different HDMI ports on the TV at different times. The line can appear when watching via any of the input devices.
The TV is, of course, now quite old but I've no reason to think that has anything to do with the problem.
Any suggestions re. the cause?