When using the Mergable filter to identify which orders can be packaged together some orders wouldn't be grouped next to each other. This issue occurred when trying to apply the Mergable filter on a view that has lots of orders in it.

We've improved the performance of this filter so that it can now be used on Views that contain up to X orders. If your current view contains more than 10,000 orders we recommend adding other filters such as Country to reduce the amount of orders.

For more information on how to use the Mergable filter check out the helpguide.