EXRCA autodiscover test failure

Preparing to configure Exchange Hybrid between the On-Prem Environment and O365 we ran the ExRCA connectivity test for outlook access.

The test fails at the autodiscover testing for XML response

Attempting to send an Autodiscover POST request to potential Autodiscover URLs.

Autodiscover settings weren't obtained when the Autodiscover POST request was sent.

The Microsoft Connectivity Analyzer is attempting to retrieve an XML Autodiscover response from URL https://autodiscover.XXXXX.com:443/Autodiscover/Autodiscover.xml for user email address removed for privacy reasons.

Additional Details

Exception details: Message: The operation has timed out

Type: System.Net.WebException

The Exchange server is published by a simple DNAT 

The On prem environment is made of two Exchage 2016 CU23 Servers in DAG .

thanks

SC