We have several extract data sources on Tableau Online that are set to refresh on a schedule via Tableau Bridge to data stored in SQL Server. Normally, each of these refreshes takes about 5-30 seconds to complete.
On occasion, however, refreshes of the larger data sources will hang and don't complete. The only way to tell this has happened is by not seeing the most recent data in the workbooks using these sources. Tableau Online doesn't appear to notify us that a refresh has failed or that it was unable to reach the data source. When the refresh doesn't complete, Tableau Bridge shows it is still performing the refresh (the timer is still running next to the data source) potentially an hour or more after it started. I then must cancel the active refresh because it is preventing the refresh of my other data sources. If I perform a manual refresh from Tableau Bridge after canceling the scheduled refresh that has taken an unusually long time to complete, the refresh completes successfully in a "normal" amount of time.
We're experiencing this issue with data sources synced to Tableau Online from two separate SQL Server machines. This seems to happen about once a day. We are using Tableau Bridge 2018.2, but I believe this was also happening before we updated.