Ah, now the file is at least in the cloud! So waiting after syncing on the iPad appears to have done at least one trick 
It is normal that it reports .flac instead of .wav, because audio files are converted to the lossless FLAC format before uploading, which saves you cloud space.
The warning on the Cubase end may also indicate that you should be patient…it may not have downloaded or copied the file yet. If you stay in Cubase for a while and then maybe try sync once more, does that work?
You may also check the VST Transit folder in your Documents folder (probably C:/Users/Henk/Documents/VST Transit), there in hippohenk/projects/audio/hippohenk2 there might be the awaited audio file (flac and/or wav). If that is so, but the warning persists, pls let us know again. Thanks!