NextGEN Gallery breaks Contact Form 7?

Hello,

first thank you for the great gallery plugin. I was very happy with this, but now I have a problem.

I have updated nggallery and contact form 7 to latest versions. Now the contact form 7 plugin is not working anymore. The response of all AJAX requests made by the contact form 7 plugin are empty. If you like to test: https://www.jugendherberge-bleckede.de/kontakt-anfrage/

It looks like nggallery breaks contact form 7, because if I disable nggallery then contact form 7 works fine.

Any ideas?

Thank you and regards.

https://www.ads-software.com/plugins/nextgen-gallery/