Fuzzy video pictures from Doorbell

I have just installed a Ring wired doorbell using my existing doorbell wiring. I also installed a Ring plug in adapter which meant soldering its wires to the existing wiring. It works but the video picture is dark. Ring technical team went through the installation on the phone with me and concluded my wifi connection was poor and recommended a wifi extender. As I already had a powerline network on the same ring main, I opted to install another nodule on that for the doorbell. There was absolutely no change in the video picture. Has anyone had a similar problem and found a solution?