Unable to create new playlists

Hello folks,

I have the problem that I can no longer create a new playlist via the web interface. If I press the plus symbol next to the heart symbol on the web interface, nothing happens.
I restored my system from a backup some time ago. I found the instructions here in the forum.

I have Volumio 2.599 running on a RaspberryPi 2 with HifiBerry.

I hope you can help me.

Greetings André