New Activity logged by user 'PowerBI' called 'DiscoverSystemDetailsofMoniker'

I'm seeing these too.

From what I can see a moniker is a reference within a dataset to a target datasource + gateway that the dataset has been set to use to access that datasource, so it's possibly the Power BI service processing a dataset refresh where it needs to get the data source details for its dataset monikers to know which gateway and datasource to connect to. The timing of bursts of these correlates well to busy refresh times in the environment.

These sure are coming through in a high volume. I wouldn't be surprised if these being included in the Activity Logs is a bug introduced in a new update; otherwise this is a high volume activity log operation and it doesn't represent a user performing an activity.

I also see a single "UpdateDatasourceCredentials" record for the PowerBI user after I updated credentials for a datasource on the gateway page.