I don't have any sound on NBC. The Roku and Xfinity app are up to date. I do get sound through YouTube TV, but not xfinity.
try the same channel using a smart phone/tablet or a desk/laptop connected to your home wifi. is there sound on the different device?
OK....so this morning I found that all 3 of my ROKU boxes were unable to produce sound on KARE11 (NBC) only!!!
I finally found this message from someone who have the same issue a few weeks ago.
CHANGE the Language on the XFINITY Roku APP to SPANISH and sound now works.
This is simply STUPID!
I don't have any idea why this works or who to report this idiocy to.