I’ve set up a complete new WordPress site. Now all is working fine. May my Database was corrupt because of testing so many plugins or by using W3 total cache.
Thanks for your help!
I guess the german market extension is the point. When I deactivate all plugins except Woocommerce + German market extension than the problem is still present, but only in connection with the enfold theme. When I activate all plugins except german market extension than I don’t have any problems.