Did you go to the link I provided? That's to the Web-based Channel Store, and when you are logged in, you should be able to use that to add it. That's not so much a work-around as it is a troubleshooting. How it responds may be important.
Go go and log in. Search for Xfinity and see what you find. You should be able to add it from there. That may cause the issues to resolve, but they are odd issues. You see Disney+ but not ESPN, which is also a Disney app. I'd expect you to see both or neither, not just one of them.
But see how searching from the Website works.
Roku Community Streaming Expert
Note: I am not a Roku employee.
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