Promoted headers but column names showing as Column1, Column2, etc

Hi everyone 

I'm trying to create a dashboard and am getting data from cvs dumps in folders (quarterly file updates).

I've 'promoted headers' under transform file / sample queries which should change the header display name.

Although this is true of the power query editor, this is not coming across when trying to apply changes and all the columns other than Source.Name come out as Column1,2,3...

I am also getting the error 0x80040E4E when trying to apply changes