After upgrading from 10.5 to 2018.2.1, Tableau always has some data connection issues ...
After I opened the workbook and choose the data source, it will take long time to do the query and failed to connect the data source.
Additionally, even I use a blank workbook and try to connect to the data source (CSV file, I just click txt files on the left, it will:
In 10.5, this doesn't happen
Hmmm. You may want to report this to Tableau Support.