Items disappearing upon filtering/including

Hi, going a bit crazy here, maybe missing the obvious? Situation is as follows:

Salestable with 'Amount' column and 'Customer ID' column

Customer table with 'customer ID' column and 'relation name' column

One to many relationship between the 2 based on the customer ID column

1 measure called 'test' as follows: SUM(Salestable[Amount])

A table report in PBI with 2 lines: customer 1 (Abdullah) and customer 2 (Company). The sales figures are the same by coincidence.

When I right click company and 'include' (or when I apply any other kind of filter to the visual and filter for the customer 'Company') the expected result is shown:

However, when I do the same for customer 'Abdullah',

the table turns blank??

Any idea what could cause this?

When I include the Customer ID columns (from the sales and from the customer table, so basically the two columns used for the relationship), and I filter 1 of both, the result does show as expected

So the issue only occures when filtering on the customer NAME column, when filtering on the customer ID column from the very same table all works fine. This makes it even more strange to me...

Any input would be greatly appreciated.