Claims identity missing in user log in token

Hi All

We are using windows claims Authenticatio in our SharePoint webapplication.

We have custom webservice deployed in sharePoint farm to update some Lists and libraries.

We are using Special service account to access web service and failed to update list items and further investigating on the logs we see claims identity is missing in the user token -->   0#.w|<domain>\<<AccountName>>  instead of i:0#.w|<domain>\<<AccountName>>.

As the claims token is missing user failed to connect to SharePoint and failed to edit lists or libraries.

If someone has come across this sisue, please let me know how this can be resolved.

Regards

Pratap