Variaudio feature disappearing

On my Cubase Pro 9 system (Mini-Mac, 16 GB memory, SSD, Sierra), Variaudio disappears completely with most files.
E.g during my last session it was visible and worked with the first audio file I tried, then with other, similar files the Flatten’ feature was displayed instead of Variaudio.
I have also seen a recommendation to use the “Segment” command in the Sampler editor before using Variaudio, but this feature is also nowhere to be seen on my system.
I know mono is preferable for Variaudio, so I converted one file to mono and imported it – same result.