Voice is dropped in ads on cable channel via OTT I am not a video expert. I used to be an audio engineer (like a 1000 years ago) and have done some video editing on my own professional grade editor for giggles but not in the last 10 years.

And yet, I am seeing something that makes me curious. So I thought I would finally ask.

I get cable over OTT via a Roku. Periodically, on channels that have minor packet loss, I have noticed that ads will lose any actor voice and the voice over portion of the content. The background and other sounds are there. Just the voices are missing. For example, an ad for a popular insurance company will have all the background sounds, however, the voice of the person in the video and the voice over announcer are gone. This does not happen for shows. It also does this for most any ad periodically and inconsistently. The same insurance ad can show again in the next ad block just fine. One ad can be missing voices, the next ad is fine, then the third ad is missing the voice. This can happen on any channel from time to time and seems to be tied to very minor packet loss. Basically, the channel is working just fine, just very minor periodic packet loss. This may be a hint.

Strange huh? Any ideas? It is not really a problem for me, just a curiosity. In fact, it is kind of nice so I am not really complaining.
I don't have a definitive answer, but what you're describing sounds like phase inversion on one of the stereo channels. This causes cancellation when heard in mono of anything centered in the mix, as an announcer voice would most likely be. Someone listening in stereo would not hear much if any difference, so I assume you're listening to a mono feed. It's hard to imagine a scenario where a commercial is delivered in a way that would separate the main channels but leave the background sound.

Why only sometimes? Speculating again, there may be one misconfigured server in a group of servers, and playout of any given spot is randomly coming from that server. It's also likely that these are local insertions, since an issue like this would probably be detected quickly at a national level.