Thanks for reaching out. Are other channels (apps) working correctly on your Roku device?
This is usually a good indicator to help you determine where the source of an issue may be coming from. Each channel provider develops and maintains their own channel on the Roku platform, including content management and delivery, authentication, etc. If you are experiencing an issue with one channel (app) that isn't occurring in other channels on your device, this is usually a good indication that there is an issue within that channel, or their services, that the channel provider will need to address.
I'd recommend following up with Xfinity customer support again to report the issue you're seeing an request additional support. In some cases they may need to review your account, your plan/service, login information etc. to ensure that it is configured properly in order to access their service. Incorrect account provisioning could lead to the type of error that you described. As a reminder, Xfinity requires that you use an Xfinity internet connection in order to stream their channel on a Roku device.
You can reach them here: https://www.xfinity.com/support/contact-us
I solved this problem by changing the Roku Video settings from Auto or 4000K at 30 FPS as supported by my TV, and setting video quality to 1080P. Hopefully Xfinity will improve their program to work well with 4K resolution through Roku, but for now, this is the only work-around I have found that consistently works well. It would be great if I could save multiple video profiles to make this easier, and allow Roku to use the Xfinity App, then work in 4K as expected with everything else.
Note, I have plenty of bandwidth and am connected to Xfinity internet. I had tried reinstalling the app and other solutions suggested in this thread. Changing video resolution to 1080P should work form most individuals experiencing the buffering problems with Xfinity App.
Are you hardwired to the TV? If not, The bandwidth you pay for, is rarely what you will get going wifi. Either way, the lowest bandwidth internet Xfinity customer should be able to stream 4k in a few rooms at a time.
Couple of real easy possible fixes to try.
Delete and reinstall roku app.
Restart the router.
Have you come across this? https://support.roku.com/article/230317588-why-is-hdcp-2-2-important-to-playing-4k-ultra-hd-or-hdr-c...
Also, the older Roku devices can't do 4k. If it is a newer one, you should be fine. You can look for a system update in setting, but they usually do it themselves.
About three days ago Comcast Xfinity Beta app quit working. When it loads it says initializing and then says "Sorry Something Went Wrong". I have deleted the app and downloaded it now a few times. I have tried updating Roku and still won't work. Anyone else having issues? Any fixes so can try?
Same issue from December 18 at midnight to present. A change in their program and it doesn't load a channel selection. I know what is wrong with it but talking to someone at Roku or Xfinity that isn't at a help desk Vietnam and has a good enough grasp of the English language is less than useless.
The issue as I see it is that the buffer that holds your channel selection is clearing before it can be transferred to Xfinity to initiate the stream. The Xfinity app comes up, the Xfinity program guide comes up just not transferring the "watch" message for that stream. How do I know this?
If you arrow back to the listing in the channel guide and hit watch again and again, they will eventually pair if the timing is right and the channel does begin to stream. It may take 10 attempts. These are simple issues a good programmer would correct immediately but I have an idea that the app is farmed out to a 3rd world country ...who knows, maybe it's the help desk working on it in between calls.