If I remember it was 2014 or 2013 when I saw the images of the Nissan GTR GT3 at "Flugplatz" get massive amounts of air.
Neither in the Porsche GT3 R's or the Audi R8 Ultra which I raced on the weekend we get this much front upforce !
I have no experience on or with the Nissan GTR so I can't comment on the aero of that car, but on the Audi and Porsche's the level of downforce for the Nordschleife is carefull adjusted so that at Flugplatz and Schwedenkreuz the car doesnt get "uplift" and dirty air.
The fact that all the top spec cars are now temporary banned from racing on the Nordschleife just shows that the authorities are now looking into the aerodynamics of the specific cars. Considering that there hasn't been any issues with airborne cars until now, I personally don't see this ban last too long.
The next VLN race will be on the 25th of April, which is also the Qualifying race for the 24h race. Give's them 3 weeks time to do the right thing.
Chris