Remove columns changes values to null

Fixed; not sure how to explain how it arose, though.

When I looked at the query output in Power Query, it looked like all the data was there at the beginning of the query (source) but that, after a given point (when I removed the fields) the two columns lost their data (all null).  This is a query that has worked for many months.

So, I removed the step which took out the columns, stepped through a few more steps, and again, the columns went from full to null.  This made me think something was a problem underneath.

So, I went back to the "source" step in Power Query, and THIS time, the interface said the data was 7 days old - did I want to refresh?  OK, yes, lets try that.  NOW, and only now, the data in the "Source" step shows the 2 suspect columns as null to start with.  This means that the data must be missing from the underlying query.

So, i go back to that query - and the data is there!  Both columns!  Huh?  For grins, I refresh the preview, and NOW the columns are null.  Problem must be the query (was pulling from an Athena datalake).

Went into the query (which I had modified late last week) and, sure enough, there was an error in the link that brought in those two columns.  Fixed that error, and now everything works fine.

So, the ultimate problem was in the underlying query; Power BI just didn't do a great job helping me figure that out.

Thanks for your help, DOLEARY85.  Your feedback was very valuable in understanding that this wasn't a normal issue, and encouraged me to keep digging.