Hello bibber,
You seem to have edited the theme. If so, back up your WordPress theme and do following steps:
1.Click on Appearance » Themes>> Activate other theme than Twenty Fifteen.
2.Again,Click on Appearance » Themes>> Hover the Mouse over Active theme>> Click the “Theme Details” button.
3.Click Next Arrow button on the top left side of theme until you find Twenty Fifteen. Click Delet ebutton
4.Go to Appearance » Themes>> Add New >>Upload Twenty Fifteen. Activate the theme.
Now, you should be able to see the themes with folded sub-items.
Next upload your content and image from your previously done back-up.
Thanks!!
Thread Starter
bibber
(@bibber)
Thank you for the answer Madhusudan, but it did not change anything!
I have now tried the theme on an other url – and the same result – apparently theres no folding of the submenu! See: http://www.soerensen.fr/birgitte.soerensen/?page_id=11