Get more info from the Cisco Meraki support team. Still the issue is working on Windows OS clients before why this is not working now. I have put comments on my support ticket. Waiting for Support to reply.
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The dashboard displays "user" based on what is supplied by the client device. In the 802.1X protocol, there are two IDs inner and outer. The dashboard can see only the outer ID as the inner ID is hidden. If no outer ID is reported by the client device then the user in the dashboard shows up as "anonymous". Note that the clients with valid credentials should still be able to authenticate and the way "user" is displayed on the dashboard should not affect that.