Hello,
You may cross check the credentials which you are using to access the Grafana dashboard.
I’m able to access the Grafana dashboard without any issue.
Note: Currently, in Azure HDInsight, Grafana is supported with the HBase, Kafka and Interactive Query cluster types. It is not supported for clusters with Enterprise Security Pack enabled.
For more details, refer “Access Grafana in Azure HDInsight”.
Hope this helps. Do let us know if you any further queries.