Not alerted when Web application is not avilable in the SCOM 2012 R2 for Azure web server

Question

Hi All,

Today we noticed an issue with one of our Azure web server.
When the web application was not available, we didn't get alerted in SCOM 2012 R2 console.
Looking at the web server under IIS role in SCOM console we see the server is in healthy state and there were no state changes too.
what can be the issue and what needs to be checked from SCOM admin side.
When we check event logs on the web application server we noticed many errors with Event ID :4151
Microsoft Monitoring Agent APM Service is inaccessible.
we are not sure if this event ID could be the reason for not alerting.
Agent health is fine on this server.
kindly assist us on this.

Regards,
Ravi Shankar