Pixels flicker when a link in a long cable run

My TV is connected to an HDMI cable with an HDMI wall socket. The cable route then covers a distance of about 8 meters, then comes the other wall socket. The cable should bridge the distance from this terminal to a computer. My previous work cable to good, but sometimes you could see green flickering pixels, depending on the screen contents.

Therefore I bought this cable, which is again 50cm shorter than my old and otherwise high shielding promises. Result unfortunately that now significantly more pixel errors.

The old cable is a no-name product. I lack the information technology and electrical engineering backgrounds, why this is so. The point is that this cable in this situation works worse than another cable that came with any device sometime times.