Went back to 12.0.279, and it does the same thing as before.
Let me describe in a little better detail:
After the Omnifi has found MC, navigation begins by navigating to the first set of categories (Playlists, Artist/Album, etc.) by arrowing right. When working properly, this list of categories can then be chosen from by arrowing right again (Choose a certain Playlist, choose a certain Artist, etc.) You then select the track you want, and play it.
With 12.0.279, I can go to the first category page, but it then freezes. There is a dot on the display that illuminates when the Omnifi is processing this dot comes up, and stays there. At this point the Omnifi must be reset in order to restart. Occasionally, it will freeze before the first category page can even be displayed.