This sounds frustrating. Have you found a solution since you posted this? I have found that the typical reason for a refresh failure is caused by a conflicting process on the database server (in my case a DB restore process that occurs each day). Is this issue encountered on Tableau Server or Desktop? What version? Are you certain that all of the current Database Drivers are in use? Are you certain there is enough local disk space?
I suggest searching on the specific details of the error - for example - https://kb.tableau.com/articles/issue/error-refresh-failed-unknown-failure-refreshing-sql-server-extract-on-tableau-serv… and determining if you can narrow down the cause more and if you are unsuccessful, then please open a ticket with Tableau Support at https://support.tableau.com