Can't install Vanilla, Show Stem Pro does not work

I have installed the Show Stem Pro module. Unfortunately it does not work. The console tells that Vanilla is missing, so I installed the modules (sorry I have german GUI) > Einstellungen > Add-ons > Module > Module installieren. I restarted Glyphs, but the error message remains:

ImportError: No module named vanilla

Someone an idea why I can’t install Vanilla?

macOS 10.11.6
Glyphs 2.5 (1131)

I made a post that contains an explanation how to manually install vanilla: Manually installing modules