I got the same error. I found a version for FireStick that solves the problem for me.
www.apkmirror.com
I have been happily running the 7.2.0.9 version until recently the app told me I needed to upgrade. and suddenly stopped working. I tried the 7.3.0.8 version posted here, but it did not work. I was able to get the above 7.3.0.9 Fire Stick version working on my Sony TV. I had to generate my own shortcut at http://atvlauncher.trekgonewild.de/index.php. Shortcut file for the above version is attached.I got the same error. I found a version for FireStick that solves the problem for me.
Xfinity Stream (Fire TV / Android TV) 7.3.0.9 (Android 7.0+) APK Download by Comcast - APKMirror
Xfinity Stream (Fire TV / Android TV) 7.3.0.9 (Android 7.0+) APK Download by Comcast - APKMirror Free and safe Android APK downloads
So after a few weeks of the update nag, 6.9.4 finally quit working. Since every file since didn't work on my MiBox3, I went and got the onn from Walmart and now I am back up on the latest version. I have no idea why the MiBox3 wouldn't work. It was at android 9 with no update pending. The onn is android 12. Just an fyi to others so they don't lose their hair trying to get an older box working.
You can use 7.4.1.6, but you will need a browser installed and a mouse to login to Xfinity.
I've already done that. I use Mouse Toggle and Chrome.
Another thing to try is mess around with your audio settings and also turn off developer options of they turned on. These two "fixes" were posted in this thread for various issues one of them might work for you.
