Nextgen-gallery conflict with contact-form 7

Hi,
Nextgen-gallery has a conflict with contact-form 7 (Version 5.0).
If both plugins are active no message appear in CF7 by clicking the send-button.
If nextgen-gallery is disabled, CF7 works ok.
You can also test it by answering the provided Quiz not correct. No message, only spinning arrow.

On a second website i disabled nextgen gallery and CF7 works nice. The configuration of the website is similar to website where the error is shown.
https://rkb-soli-nrw.de/kontakt

Other website (other Provider) where the error is shown:
https://rcbrheinhausen.de/kontakt-anfahrt/

Nextgen Gallery, when activated, works ok for me,
CF7, when activated witout Nextgen gallery, works nice also.

The page I need help with: [log in to see the link]