|LCD screens cheat how they use display chips. They re-use some chips to paint part of the screen and then the next part and so on. I suspect that side board is going bad.|
It may be a poor connection in the display too.
It is not easy for most people to fix. An expensive part is needed to attempt a guess unless you have many parts for test use.
Make backups daily or more often and when it dies buy a new system.
Hang up and live.