Paginated reports published in a Premium per User cannot be seen anymore

This error message indicates that there is an issue with the connection to the data source used by the paginated reports. There are a few things you can try to resolve the issue:

1. Check the data source connection: Make sure that the data source connection is still valid and that the credentials used to connect to the data source are correct.

2. Check the gateway: Make sure that the gateway is configured correctly and that it is running properly. Check the logs for any errors or warnings related to the data source connection.

3. Check the Analysis Services instance: Make sure that the Analysis Services instance used by the paginated reports is running properly and that there are no errors or issues with the instance.

4. Check the permissions: Make sure that the users have the correct permissions to access the data source and the paginated reports.

5. Check for updates: Make sure that both Power BI and the Report Server are up to date.

6. Check the firewall: Make sure that the firewall is not blocking the connection between Power BI and the data source.

7. Check the network: Make sure that there is no network issue that is preventing Power BI from connecting to the data source.

8. Try to recreate the data source: Sometimes the issue is related to the data source, try to recreate the data source, and check if the error is still appearing.

If none of the above solutions work, it's recommended to open a support case with Microsoft to get further assistance.

It's also important to check the Power BI and the Report Server logs for more details about the error and provide this information to the support team.