Merge in Power Query not working

Hi guys,

i have two tables that i am merging in the power query editor via -> merge queries menu. I'm joining the two tables via an article number column. All article numbers are in the second table. So the first table shouldn't have any blank rows for the join. 

But for some article numbers the join does not work. Now the weird thing is that if i do the same join but via LOOKUPVALUE formular all items get a match value. 

Data type for both colums is text. 

Anybody an idea why it works with LOOKUPVALUE but not via the merge queries function in power query?

Thx!