Unfortunately the desktop version of our website is not running. There is a strange error in the console.
Have a look: 2017.mono-space.com
It appeared after saving the permalinks settings page - pretty links are applied.
One more thing which might help identifying the error:
Before the whole website broke, the projects category archive page had ‘category’ inside of the url right before the actual category slug.
Besides that some pages are running regularly. Also single projects are displayed correctly.
Thanks for your help. Much appreciated.
Edit: I was able to restore the functionality by saving the affected pages after a simple change like adding an empty row.
But still the having 'category' in the slug, which wasn't there before.