SEP clients not doing reputation check with ATP on https 443 port.
ATP 2.3.0 doesn't support port 443 for reputation.
Till ATP 2.3.0 version we use https on 8443 port.
However, from ATP 3.0 we are planning to support 443 port and Port 80 will not be supported.
Note: Changing to HTTPS in the SEPM is not sufficient, we have to create the certificate in the ATP under "Secure Endpoint Traffic panel". Please check the ATP Admin guide.