Sony TV Screen Goaes 75% Darker

I have a Sony 55 inch LED TV that is about 10 years old. It has worked great that whole time, but recently I'm having some issues. If you turn on the TV it will work great all day with no issues, but if you turn it off and then back on it will go darker on 75% of the right side. The other 25% is still normal. After letting it sit off for a while, usually next day, it again will work fine all day, until you try to turn it off and back on.

I have taken the TV apart and removed the connecting leads and cleaned them all, but it did not fix the issue. I'm thinking it may be a bad T-Con board, but not sure how to test it. It could also just be a bad panel.