After adding a new datasource to an existing report and republishing, I get prompted to configure the new datasource (a network folder path) and configure our enterprise gateway accordingly.
When returning to the dataset settings, I map the new datasource to the new entry in the gateway. All of the datasources are now mapped (the new datasource and existing previously mapped datasource).
The issue is that the radio button that allows selecting the gateway is not active even though all datasources are mapped and thus the 'Apply' button is not available.
Publishing a copy of the pbix and mapping the all the same datasources to the same gateway from scratch works. The radio button for the gateway becomes active after you map the last datasource, so the bug may be that the radio button only becomes active after the last datasource is selected. When you are just adding an additional datasource that is not the last in the datasource list, the radio button for the gateway does not become active.
Before adding this new datasource, the dataset has been successfully updating on a schedule through the same gateway - the problem is just that I cannot re-select the same gateway after setting up the new datasource.