Cubase 8.5 Crash after Startup (White Screen flickering)

Hi Guys,

I recently updated my iMac to El Capitan and Cubase Pro to 8.5.
Since then there have been several crashes while using iZotope RX4 and since this morning I tried several times to open Cubase but it always crashed. I needed 5 attempts to make it run.
The crash looks like this: After loading up Cubase and scanning all Plugins (everything works perfectly to this point), it just shows me a white screen which is flickering for a few seconds and then it says “Cubase quit unexpectedly” or something.
I read about a similar problem regarding not enough RAM. Im running Cubase in 64-Bit Mode and my iMac has 24gb RAM so i think this can’t be the solution.

Anybody have any idea how to fix this or what kind of problem this can be?