Refresh Now and Scheduled Refresh Not Working

Thanks Herbert for your answer,

After several tests we fixed the issue.

When the spreadsheet is connected to the PowerBI service its “Data source credentials” displays the following message:

 Your data source can't be refreshed because the credentials are invalid. Please update your credentials and try again.

The message above is misleading because the report can refresh without updating credentials. In fact, updating the credentials is what prevents the report to refresh.

I think that this is why the original report stopped working. When we created a new copy (without any modification at all) and we connected it to the PowerBI service we also updated its data source credentials (following the message). I think that the PowerBI service linked both copies (the original and the new one) to the same data source and when we updated the credentials of the data source on the new copy the change affected as well the original report preventing both from refreshing.

The above information are suppositions based on our tests and observations. It may be good that the development team behind the product was aware of it for further investigation.