iOS client: missing media transport icons

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.

The progress bar will appear after click at the bottom of that window.

That’s definitely not true. What versions are you using? I’m running seafile app 2.5.7 on iOS 10.3.1.
As you see, there’s only a black window with a horizontal line when I open an audio file. I can touch the display wherever I want: no buttons and no progress bar appear.