Note: this is not a request for troubleshooting help.
For the past few years my 10ish year old “smart” TV will maybe once a week or so completely lose the ability to play sound in the Youtube app, and only in the Youtube app. Sound works just fine everywhere else. Bizarrely this is always triggered by an ad and never a video. Restarting the app doesn’t fix it, and neither does clearing the cache. Fortunately doing a full restart of the TV fixes it, it’s just irritating to have to restart because an ad somehow broke the sound.
What technological gremlins haunt you?
It sounds like a defect.
I would vote (in this order)
Bad capacitor moves up on the list if it wasn’t happening and is getting more profound or if you are having other stability issues.
While I bet you have had it for a while, thiswould be enough for me to try a warranty claim. The problem could lead to other issues.