I got a trouble with my Samsung UE55KU6450 Smart TV (4 years old):

When I turn on TV, screen works fine in the begining, but vertical shadow stripe appears a few later.

I note the same area at the rear of the TV is a little hot, as the bottom front.

I've tried auto image testing and trouble remains in all tests.

You will find the same issue been frequently reported in Google for different series of Samsung TVs, but not given a technical reason explaining what's up, nor a solution. Is it a LED stripe problem? A electrical issue?  Could it be due to heat dissipation or panel pressure adjustment issues?