Right Anti Join Returns Null

Hi there!

I have 2 tables containing a list of parts, one from last month (Old, 165658 rows) and another from this month (New, 166761 rows). I want to do a right anti join so I can only display the rows from "New" that are different from "Old". So I go to the power query editor --> merge queries --> merge queries as new. See the image below:

Column 2 is the matching column, there are 165566 matches. The result is just a table of null values. (See the next image).

Could someone please tell me what I'm doing wrong? 

Thanks!