It happens frequently (up to 10 times an hour) and it comes right after a couple of minutes of retrying. This is the whole message that I receive:
It happens on the website, as well as the cpanel and the Wordpress back-end.
"The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.
Additionally, a 503 Service Unavailable error was encountered while trying to use an ErrorDocument to handle the request."