I had this issue for the longest time. Went through multiple boxes with no change. Tried everyting that was described about settings and nothing changed. I finally found a solution that has worked for me for over the last 6 months and thought I would share, hopefully this will help some.
I found the issue had to deal with universal remotes. If I were to turn off and on the TV with the Xfinity remote I had no issues. I noticed it was only an issue with my TVs universal remote if I used to it turn the TV on or off. I have a Samsung TV with a universal remote and when the TV detects a new device on an input it automatically goes through and sets up the remote. You do have the option to skip the universal remote set up or remove it. Once I did this I have not had any issues with the black screen. Only downfall is you will not be able to use your TVs remote to control your cable box.
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