Hello Leo. So it works flawlessly for me. For what purpose did you want to use this coupling? PC => Monitor/TV or what? In my case it's PC => monitor including sound and it works great.
I think it's because the two HDMI cables I want to connect are too long, because when I connected two shorter ones it worked, but since I want to connect a 10m cable to a 3m cable, it could be that the length is a problem.