If you are a Server Admin on the Tableau Server, you will have access to the following:
If you select "Maintenance", then "Background Tasks", you will get a dashboard with all of the tasks being run by the Tableau Server. If you look at the appropriate times you "thought" the extract was refresing, you will be able to scroll over the observation, and get a description. You are probably running out of storage space, which is aborting the refresh.
Hope this helps,