It's not very clear what are you describing...
Do you have extract-based datasources? Do you have schedules? Do refreshes fail or just don't happen?
It is extract-based datasource. Refresh doesn't happen. I tried to execute a full refresh.
And what happens? Does it fail? If yes - how? Any specific error message?
What's the live connection behind this extract-based datasource? What database? What authentication type does it use?
Start by going to your Tableau Workbook on Tableau Server and under the tab 'Data Sources'
Click on the connection you want to use and test the connection to your server.
If this also fails it means you don't have the right driver installed, you are using the wrong credentials or a firewall is blocking the access to your server.