Spinning wheel stuck

I write same question, responding to other thread.
Occasionally (but often once a day) user try to send form but spinning wheel stuck. I check also leaving blank required fields and wheel stuck with no red-border warning. So I assume has nothing to do with email smtp process. Then I (admin) must go in WP dashboard, edit contact form and save it (just save, nothing else). Then retry as above an red-border warning appear. Then fill required fields and contact form works.
What’s solution to this matter?
Users claims for no working website contact form, if I’m not able to access WP and do.

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