At the end of August last year I received an email from the Australian distributor of Denon and Marantz regarding problems with the new Foxtel (Australian Pay TV provider) IQ4 4K set top boxes. These involve HDCP2.2 issues.
It goes on to say that they have been in contact with the head of (Foxtel) engineering and it has been confirmed that there is a glitch in their firmware.

The email went on to say that there was expected to be a firmware update available in October 2018 or, this is no typo, March 2019. A discussion that I have since had with tech support, evidently Foxtel does ALL of its testing with the STB connected directly to the screen/TV. There is no testing done with an AV Receiver, much less a Matrix Switch, they don't know/care.

So, unfortunately it sounds like you guys in the US are suffering a similar problem, it probably is a engineering/firmware problem like we have here in Australia, the huge problem is likely to be getting them, Comcast, etc to acknowledge the problem and then to do something about it.

The short term solution offered by the distributors is either connect the box directly to the screen and use optical back to the receiver, obviously no good if there is a Matrix Switch involved, or to use a product like the Blustream HDCP11AB, I'm sure that you guys in the US will be able to source a similar problem.