This release fixes bugs with UDM devices using Prometheus. It changes the data structure for all device graphs using Prometheus (UAP, UDM, USW) and you'll need to update your dashboards yet again (just those 3, and only if you use Prometheus, influx is unchanged).
Also included are some data storage fixes: counters were consolidated and superfluous tags removed - which should improve storage requirements for prometheus.
Please see the release 1.6 release notes if you haven't yet.