I did some research on the behavior and the error message being presented and there is some investigation currently going on around this error.
Please submit a case to the support team if you have not already: Support Case | Tableau Software
Additionally, as troubleshooting step, does upgrading the workbook in Tableau Desktop (Opening the 10.3 workbook in Tableau Desktop 2018.2), allow for the connection to work as expected? Another step to try would be to rebuild the connection in Tableau Desktop 2018.2
Hope this helps!
Thanks Patrick for the update. actually I was able to resolve issue. I was trying to refresh data on wifi connection. So bandwidth was the issue. After connecting to network I was able to refresh and upgrade successfully.
I am happy to hear that you found a solution.