Discovered something very strange...
If I have a Custom Dimension set up in GA, as soon as I include it in the dataset, it throws off all my data.
If I set these up:
It returns this:
...as SOON as I add Custom Dimension 1 as a dimension, without doing anything on the worksheet, it changes the data to:
Turns out this is a Google Analytics issue, NOT a Tableau issue.
Retrieving data ...