Failed use of Mixer in 2.9.9-2.9.11

While using Musescore also on my mobile (using .mscz files as mailed from my desktop, generated from OS: Windows 10 (10.0), Arch.: x86_64, MuseScore version (64-bit): 3.6.2.548021803, revision: 3224f34); I can't select which bar (music instrument) I want to see. Before it was possible to select one or more specific bars. Now the mixer function on my mobile stays blank. This makes the app for me useless so please release an urgent fix. I just updated my app on my phone to your latest release 2.9.11 but this did not give a solution on this problem