Hey there! I'm not sure if there is much we can do on the cPanel side of things for a 404 error. There would need to be some additional troubleshooting performed on the server where the sites are hosted. After you created the index.html file, does the Apache log show the 404 page being served from the correct document root? If you have mod_userdir active on the machine, can you visit the page with IP/~username/index.html?