Hi, I don't know when this happened, but I assume it was the latest update of the iOS client (2.5.7) a few days ago.
Before that, when playing audio files, there were transport icons available (play, stop, etc.). Now these icons are missing. There's only a black window with a grey horizontal line. When I click on an mp3 file, the file starts playing, but it cannot be stopped anymore. The progression bar is also missing.