GROUP BY in PowerQuery ignores 1 specific value

Hey everybody,

I'm either missing something extremely obvious, or I've come across a bug in PowerQuery.

I'm creating a table of clients, their orders and the products in those orders. While trying to use a Group By of all clients and their last orders, 1 clientnumber dissapears.

To test if I've done anything wrong, this was my debugging process:

1: From the current state, I filter the column clientnumber to CONTAINS '#' (the missing client). This shows me 1 line with the client and their order.

2: I now use the Group By function on the column clientnumber without the filter. As aggregation I used count rows. If I filter the resulting table on clientnumber, again with CONTAINS '#'. This gives a table with no entries, meaning that the value that was there before is not included in the Group By.

3: To double check, I used groupby on the filtered table (so 1 row) and then if obviously works.

So the groupby only includes this specific client if I filter the data to only include their clientnumber. If I do not add this filter, they are skipped.

Am I missing something obvious? Sorry for not including screenshots/actual values, since it is confidential information. If needed, I can try to obscure parts and include them

Kind regards,

Sidney