Hello and welcome, @justinpbrown
Diaspora doesn’t have any official apps. There are a number of thrid-party apps but basically all they do - they display Diaspora normal mobile pages and add some bells and whistles. It is hard to provide troubleshooting for unknown third-party apps.
I would recommend trying to just open Diaspora in Firefox or Chrome - it will have pretty app-like experience, especially if you create a screen shortcut.
If you really want an app for Android then Dandelion from F-droid store is pretty good. The version in official Play store was a bit obsolete last time I checked it.
Also note that data usage directly depends on what is in your stream. Diaspora mobile view has some optimizations but if your contacts post a lot of high-resolution images (especially if they embed them inline) it will use up traffic but this is the case with any website.