Mac latest, desktop app, community-daily.
This seems to only happens if the server is the first tab. The server in the first tab will not have a zoom icon in the channel header. The server in the second tab will. This happens even if both servers are community-daily, or if they are different servers.
1. Start with no servers.
1. Add community-daily. See there is no zoom button.
1. Add another community-daily. See that this second one has a zoom button.
Update: this is happening on every community-daily (for me at least), even when multiple daily servers are loaded.