Issue:
When Testing the Hybrid Connectivity using the below Command,
Test-HybridConnectivity testO365Endpoints

Resolution:
Checked with Microsoft by raising Support case. It seems that the host watchdog.servicebus.windows.net is no longer . Which is why it could not be reached.
To resolve this issue, as recommend by Microsoft, commented out the line in PowerShell script and now it is completed without any issue.
Hi,
Can you post screenshot of which line was commented out. I am also getting same error.