Ocassionally ,all sharepoint 2010 web applications prompting for credentials multiple times

Hello ,

  We have multiple web applications created on Sharepoint 2010 server . When login with windows credentials and access few of the links on the sites ,system prompts for credentials and even after providing credentials it server will never authenticate and lets us inside.And this happens occassionally. For the first attempt we were able to login without issues .

For one of the sites when checked fiddler trace we found that server is not  generating challenge at times.

We have followed below steps

->Disabled loopback check

->Added sites to trusted zone

->Checked LMCompatibilityLevel at all the places (Client,WFE and Domain Controller end)

Request help to identify what else could cause server not to generate challenge when request comes from client?Thanks