Forms Not Submitting – 500 Error

On some forms, when the user clicks submit the form just hands and the spinner continues indefinitely with the form never submitting.

A review of the Console shows:

http://wordpress-178883-527713.cloudwaysapps.com/wp-json/contact-form-7/v1/contact-forms/7619/feedback 500 (Internal Server Error)

We were able to disable the Rcwd upload plugin and the form submitted correctly. But we were able to use that plugin just fine before a recent server migration.

I also tried to use a default htaccess file in case something there was causing the problem.

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