AJAX Stops Working with Contact Form 7

YES! Actually, thank you so much for creating this post. I’ve noticed this AJAX error because Google Analytics just stopped recording the contact form event from one day to the next. I really didn’t know where to look at next.
So, thanks to your hint, I just deactivated “Invisible recaptcha” plugin, and suddenly the contact forms are working again!

Actually, that Invisible RC plugin has not been tested with the latest versions of WordPress. Looking at its changelog from the past, apparently, there have been reports of AJAX-related issues: https://wordpress.org/support/topic/problem-with-ajax-after-update/

Also, this update has not been tested with the last 3 major WordPress updates, as discussed here: https://wordpress.org/support/topic/this-plugin-hasnt-been-tested-with-latest-3-major-releases-of-wp/

So, I’d recommend to avoid it for the time being.