This post is a follow-up to my support request. I was able to fix my issue by performing a factory reset followed by a hard power cycle (I unplugged it) with a 10 second delay before plugging it back in. My firmware successfully updated over WiFi before this issue appeared. I did not try a flash drive update.
I have since had two instances where the soundbar stopped playing audio from the TV. A hard power cycle fixed both of these as well. Hopefully this is just a firmware issue that will be updated at some point.