Contact forms not submitting

What other plugins and theme do you use on the site?

I’m using the theme enfold 4.5.7 and a bunch of plugins – askimet anti-spam, anti-spam by cleantalk, better font awesome, classic editor, contact form 7, duplicate page, hustle, insert headers and footers, ithemes security pro, list category posts, loginizer, managewp-worker, pro-categories widget, really simple ssl, simple calendar, smush, wp add custom css, wprocket, wpforms lite, wpmu dev dashboard, and yoast seo.

Try switching to the default theme and deactivating all plugins excluding Contact Form 7, Akismet, Classic Editor, and Yoast SEO.

Why you are advised to deactivate plugins and switch to the default theme.