So you have a 4K TV. Let's try a couple of experiments.
1. Set the video output to 1080i only (which makes the TV do all upscaling to 2160p)
2. Set the video output to 2160p only (which makes the V6 do all upscaling to 2160p)
Is there a difference when you view an HD channel such as BBC1 HD?
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Hub 3.0, TP-Link Archer C8, TP-Link TL-SG108S 8-port gigabit switch, V6