What has changed is that the complete Viewport code was re-written.
The following are just standard steps, I assume you have checked them already, but since we are in a forum, I like to list them:
Viewport Hardware is now the old OpenGl Preference
In the Editor View> Options> Enhanced OpenGL should be on with the other qualities you like to have.
Resize the Viewport to half (just to gain more ideas about the problem). Is the Editor and Picture Viewer the same?
Are all Graphics Driver on the latest build? IS the Cinema 4D on the last build?
Anything else is certainly a case for the support:
My best wishes