Regarding the vertical lines in the color bars... I have found out this lines are actually there in the PNG file I got from the screen capture. So it just seems the test pattern has these vertical lines in them, maybe SupportAssist uses a compressed image. So this issue can be ignored, and should definitely not be a reason to swap my LCD screen!
You might wonder why I didn't see the vertical lines on the external TV. Turns out they are actually there, just very faintly.