Send button not working anymore

Dear WPForms,

the contact form linked above has always worked smoothly. All of a sudden the send button has stopped working. I’ve tried the following without success:

• disabled any other plugin
• disabled the current theme
• website cache cleaned
• web browser cache cleaned
• blocked cache/optimization for that page
• disabled captcha / spam filters
• created a duplicate copy and removed some sections

The problem is only in that single module, while other modules in the same website work correctly.

I cannot see any specific error message logged in the console nor in the wpforms logs (where I can see only effectively sent modules).

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