Helping one of colleague from CWA team on the issue where browsing any static content[htm/jpg] is ending with blank white screen on the browser.
That prompted me to look into IIS logs . Here we saw 500 0 1346. As the next troubleshooting step we configure FREB for the 500 error code.

Here we see :

ModuleName IIS Web Core
Notification 2
HttpStatus 500
HttpReason Internal Server Error
HttpSubStatus 0
ErrorCode 2147943746
ConfigExceptionInfo 
Notification AUTHENTICATE_REQUEST
ErrorCode Either a required impersonation level was not provided, or the provided impersonation level is invalid. (0x80070542)

Authentication:: anonymous
User from token:: NT AUTHORITY\IUSR

That means we are using Anonymous access and the credential token passed as NT AUTHORITY\IUSR

Resolution provided was to make sure

The IIS_IUSRS group should be in  "Impersonate a client after authentication" in the local security policy.