I just got mobile app ios Version 4.2.15. Seems like the last row of controls are missing - all three volume buttons. Is this the new version? The picture on the app store has a different remote. I wanted the mute button.
You get a different set of controls based on Roku model (TV and/or Set-top-box). I imagine the mute button would be specific to the Roku TV models. In my case the Private listening button is removed on models that don't support it.
I just got an Express + and use the Android app's virtual remote to channel sound to my headphones. I sometimes see the bottom row of audio control buttons you are referring to when I first select the remote in the mobile app, but then they disappear.
Sometimes this seems to happen as soon as I hit the headphone button on the virtual remote for private listening (which makes no sense - why wouldn't I need muting just because I'm wearing headphones?).
However, at other times the bottom row of audio control buttons don't appear at all, even when I haven't activated private listening, so it isn't clear whether use of headphones is actually related to the disappearing row of audio buttons or not.
Apparently direct support isn't included with my device (which was not made clear to me before I bought it), so I'm hoping someone who does have access to Roku support might have reported this bug, and received some idea of the timeline for fixing it. If not, I guess my only option for communicating the issue to Roku is a negative rating of the app on GooglePlay.