I don't know why you switched from an Apple TV to a Fire TV device, but if your primary usage of the device is with Channels, I would recommend you switch back to the Apple TV.
The Apple TV is the primary development target of Channels, and all new features come to that platform first. (Other Apple devices get the features next, ultimately followed by Android/Fire OS devices; in fact, there are features the Apple TV client has that still have yet to appear on Android-based devices.) So, unless there was some particular reason that drive you to switch platforms, if Channels is your primary use-case, then I suggest switching back.
Not gonna happen here. I have faith the devs will smooth this out eventually. So far this doesn't seem to be a widespread issue either, and I don't want to discourage anyone from trying Fire TV.