Extract right 6 characters returns incorrect data

When you look at the columns used in the relationship in the data view, highlight each column and confirm that the # of distinct values is the same as the # of rows in the column to be used on the 1 side of the 1:M relationship.  You mentioned that your data has letters in it too.  Note that M is case sensitive but DAX is not, so even if you remove duplicates in your query, you may get there error if you don't first change everything to UPPER or lower case before you remove duplicates.  You can also add a step to remove empty rows (in Remove Rows pull down).

Pat