Found the answer to this. The reason this was happening was because yarn.timeline-service.entity-group-fs-store.group-id-plugin-classes in yarn-site.xml was blank.
I updated the cluster with the correct config below and restarted required services. And now its working!
yarn.timeline-service.entity-group-fs-store.group-id-plugin-classes = org.apache.tez.dag.history.logging.ats.TimelineCachePluginImpl.