Do you have the flow open in Tableau Desktop? If so, you have to close Desktop first and then refresh.
Hi-- everything close; I always run flows with desktop closed.
I'm having a similar issue.
I'm on a new computer (MacOSX 14). Pointing to data sources I've used fine in the past.
All connections, calculations, steps, and unions show no errors. (although there is one error at the upper right of the window).
The field list/table in the bottom right is blank on everything.
Opening a new Tableau Prep workflow seems to connect and display the field list/table OK.
I wish I could copy/paste elements from the problem-workflow to a new one. But Tableau Prep doesn't seem to let you do that.
Did you uncheck columns in the source file ? I had experienced similar issues when i was directly preparing prep file which had around 50M records for performance testing.I had to download data into CSV files and prepare the .tfl.