Video shows but there is no audio on 17.6 android box. Using the same device to cast, I get audio and video on 16.1 android box.
Kodi has no casting support unless you're talking about UPNP/DLNA. So if you're having issues with miracast, it's not related to Kodi but the Android OS underneath. You have to contact the product vendor/seller for support in this case, since we don't build or sell any Android boxes (or other HW with Kodi pre-installed).