Just a quick headsup about this. Today was my first day in the studio again in the new year and so far I didn’t run into the issue any more after the update/reinstall of my video drivers. So I guess that the issues where indeed coming from the videocard drivers.
If the problem comes back again I will let you know, but I guess it’s solved 
Well, i experience the same problems still with Wavelab 9.5’s Masterrig only, so i will stick with WL 9.1 and Cubase 9 for now.
I’m afraid that it didn’t work… I had the issue again just a couple of minutes ago. 
Since i’m not the only one having this issue, there must be something wrong here.