Upgrade to 7.9 causes graphical Problems in Menu Bar - see Screenshot

Hello, hope you can help me.
I just upgraded to the latest release directly through the Update Assistant. Now the Menu Bar is kind of destroyed, because I have several lines of the same items such as search, admin, … See Screenshot.

Does anybody have an idea how I can get the correct view of the menu bar, that means just one line with the items?
Your help is really appreciated.

If you are upgrading from a version that doesn’t use SASS. A hard refresh and clearing cache will fix this