Hi, you can try to load it step by step and check wich join is giving you the empty rows, the you can check that data to see why the join is not working as expected. If you are sure that there is data for all the customers on the first load maybe it's a format issue: the codes on a qvd are stored as number and the other has them stored as string.

You can also try to load the join that fails as another table with another field names to compare values and check why some customers are not joining the data.