Cubase won't quit

Cubase 9 won’t quit anymore. I always have to force quit.
I checked the forum, but I found only one discussion about the same topic for Cubase 6 with a link which does not work anymore.
Any ideas?

MacBook Pro, Mid 2010, Sierra 10.12.5
2.53GHz, 4GB memory, Babyface


What happens instead? Any message or…?

Is it the same if you close the project before? Is it the same if you write from menu or Key Command or GUI?

Thanks, Martin,
It happens with any file, even if I try to quit in the Hub, before setting up a new or old project. No message except the usual ‘won’t quit’. Haven’t tried the key command yet. Will do.
Wavelab doesn’t have this problem. MS Word 2011 had it occassionally a while ago, but I don’t use it regularly.
Also, I can’t access Wavelab 9 from within Cubase 9, a problem I reported a while ago. But I don’t think it’s related to ‘no quitting’