Two data sources on the same imported dashboard do not work

Version 7.3.1. I am importing dashboard 928 and connecting it to an Influx database successfully. The top left shows the data source name. I add a new data source and change it in the same dashboard but the contents do not change. I try importing 928 again with the new datasource but there is now no data reflected in the dashboard. I change the data store to the working datastore but it still shows no data. Evidently the datasource on import cannot be changed.

What am i missing since both datasources show successful and the measurements in the databases are the same and contain data?

Is there a way to ‘execute’ a datastore to see what it provides to the dashboard?