That's multiple variables, so you need to pin down what is actually causing the issue...
If you have buds, I suggest linking buds to AppleTV to cut out the rest and watch some movies on Netflix or Amazon Prime. Will audio cut out on them? If so, you'll know the problem is probably AppleTV (or maybe broadband or wifi). If not...
Add one more link to the chain. For example, use the TV speakers instead of the soundbar and watch movies from those services. Will audio cut out that way? If so, the TV needs more scrutiny. If not...
Check your connections. HDMI ARC from TV to Soundbar? Or something else? HDMI from AppleTV to NOT HDMI Arc on the TV. If all that looks right...
Swap in some other HDMI cables to try to rule out cable issues. Old HDMI cables and/or cheap ones from who knows when/where can sometimes be at fault with newer, modern signals. Swap one cable at a time and then watch a movie and see if sound drops out. Throughout all of this, you are trying to change just one thing at a time so you know which link in the chain is the cause.
Beyond all of this, carefully check your settings on everything.
One more thing: can you find any movie or show where it always drops out at the same time? If so, that can be an ideal test video to run through one-variable-at-a-time changes (unless that one video itself is at fault). If your TV has some "smarts" run the same apps on it and use the same video to see if TV to soundbar will cut out audio.
Once you pin down exactly what is the cause, you can dig in much harder to resolve it.