As discussed in this forum under a different thread, my system does a similar malfunction. This morning the channel I was watching (DirecTV) just muted. Changing the feed (I was watching CNN) to the next station and back brought the sound back. Yesterday, on a different receiver, but watching on the channel DirecTV and CNN, the sound amplification jumped so loud that the speakers distorted. I corrected it using the same method. Thus, I do not believe it is an amplifier issue. It appears to be a software issue. Here is some information from today:
Model 4660RW - Roku Ultra
Serial Number: YJ0050057354 (CS4895057354)
Software Version: 10.5.0 build 4208-46
Timestamp: 2021-12-23T13:57:05Z
ID: 54-513-477
Channel Version 3.27 build 3030101
Also, this Roku Ultra model keeps reminding me to insert a SD chip for extra memory. However, it does not have a SD chip slot, so the message is moot.