I have channels installed on my Shield device and it is version # 2021.02.09.1725.
I have some videos downloaded from a specific downloader from Amazon. For some reason those videos will not play the audio when I use the Channels app on the Shield TV. The audio plays back fine in the web browser for Channels. It will also playback fine in Emby on the Shield TV.
I submitted diagnostics from within the App on the Shield. I also changed the playback mode from "Software" to "Hardware" in case that helped but it didn't. I have it on Software due to the bug playing back NBC or CBS channels or recordings.
I so far have only downloaded two shows from this software and both are acting this way.
Let me know if you need something else.