Hello, I connected the monitor to an iPad Pro 12.9 2017 while working in the dark. Since the iPad PRO does not support 4K external display, there were black borders on both sides of the screen. When I turned off the iPad and before the screen of this 43" got turned off, I saw a block (in purple blue) on the lower right region of the screen. What is that? Is my monitor defective? Anybody else has this problem?