If you are using a live data connection in a workbook, then PushMetrics might be unable to export the data and you will see a error message like "Problem creating image" or similar.
In most cases, Tableau returns an HTTP 406 error or an HTTP 500 error to PushMetrics.
To resolve this issue, try to embed the database credentials for your data source upon publishing your Tableau workbook to the server.
By default, views connected to live data require users to log in to the data source with a database username and password. If you discover that PushMetrics is unable to pull data from these views, then the problem is most likely that live data is requiring a separate set of credentials to access.
You can work around this if you configure Tableau Server to embed these database credentials, so that PushMetrics can pass through the login process and go directly to the view.
Please note that this will NOT store your database credentials in the .twb files or expose them to us in any way. Embedded database credentials are stored encrypted on the Tableau Server, not in the workbook file.
You can check Tableau's documentation here to learn how to embed database credentials.