I am not seeing much of anything in the posted image. I do see the color at the right edge of the Flat frame. I can also see the effects of that colored area that the Flat impressed onto the Light due to incomplete (under-corrected) calibration.
The Flat appears to be showing some vignetting on the right side of the image. That is not due to a sensor or camera issue. Such a shadow can be normal an is usually caused by something intruding into the light path of the optical system. The "off" color of that shadow could be caused by any filters in the optical system or in extreme cases by off axis color due to some miss-collimation in the optics.
I downloaded the Flat and see no evidence of any dead pixels. The red channel of the flat is the weakest while the green channel is the strongest. They are all in good ranges. This is all very normal. Below is a Contour Plot of the Flat frame. You can see the effects of the slight vertical vignetting at the right side but the Flat will remove any similar vignetting from your Lights. That is why we use Flats, after all.
In net, there is nothing that I see wrong with the Flat. So long as Flat frames reflect the true condition of the optical system, as this one does, they will work and how they look doesn't matter. You can see lots of very ugly Flats here on CloudyNights and yet they do their job of removing those unwanted optical characteristics from their corresponding Lights.