Background: I was using an older model Fire TV Stick 4K that was plugged into my receiver, which was then connected to my Samsung 4K tv (2016 model). We recently did some reconfiguring and I purchased a new Samsung 4K tv and plugged the Fire TV Stick 4K directly into the TV. The sound started periodically dropping out, with the only remedy being to restart the Fire TV Stick. I first thought this might be an issue with the TV itself (since it never happened on the previous TV) but restarting the Fire Stick always worked and native apps in the TV played with sound just fine even when audio dropped out on the Fire Stick.
I purchased the newest 4K Fire Stick, but it had the same issues. As a last resort, I switched to an Apple 4K TV that was given to us by a friend. I do not like the user interface nearly as much as the Fire Stick, but there are no sound issues, so I'm kind of stuck using the Apple TV unless the sound issues can be resolved with the Fire Stick.
I fiddled around with changing audio output and all that but to no avail.