I have already approached them and this is what they say:
We have sent several test submissions with the contact form, and we’ve been able to find when your site is pointing to Cloudflare, we are able to replicate the 520 error, however, when we point our hosts file directly to the server (this removes Cloudflare from the navigation for us locally) there are no errors, and we receive a pop up stating that the message was successfully sent.
We also are not seeing logs on the server’s end indicating an issue with the contact form itself. This leads us to believe that there is something on Cloudflare’s end creating an issue with the connection specifically when the form is attempting to send. As we do not manage the Cloudflare installation, we would not be able to view the logs on their end in order to determine exactly what is being blocked. You would need to reach out to Cloudflare’s support to see if they have more detailed logging in regards to this issue.