Double key join results in blank dataset

UserBird

I am trying to joint two csv datasets based on two numeric keys. Checked consistency between meaning and data format, and all kinds of different types of join, and in all cases I get a log saying over 340 thousand records have been added, but no row is shown in the explorer. Always says "no matching rows", even though I am left joining, in which case at least the left dataset rows should appear.

It is as if the resulting dataset is empty. Could not find a clue in the log and had to move to another platform in order to perform the join.

Thanks

Reinaldo