"Web server is returning an unknown error" Cpanel web application run with Cloudfare SSL

Does anyone know some troubleshooting I can do for the attached error? - This is a web application run on CPanel web server using Cloudfare for the SSL - This error happened quite randomly as I have not made alterations to my website in months. - CPU usage seems normal and is not at high levels. - It is intermittent and happens every 3 or so requests - Happens on multiple requesting devices on multiple networks Any help would be greatly appreciated.