Given your relationship, there is no need for the portal filter. I'd remove it.
How many portal rows are there in your portal when you check the settings in Portal Setup?
Is it possible that you have only a one row portal and thus the other items are there but they can't be seen in the portal?
Have you checked the values in the match fields to make sure that they have the correct values?
Have you considered a list view of your data based on the item table?
Such could list your boxes and their contents much more efficiently by putting fields from Box in a sub summary layout part and listing the items beneath them. Such a layout will automatically adjust for differing numbers of items in your boxes.
Thank you for your answer.
I removed the portal filter and I have 4 portal rows per portal.
I have a counter (another field is a calculation in my box table) that shows the number of items that have the corresponding boxID and it works fine so I am sure that I have several items with the same boxID.
The problem with a list of portals in the item table is that I will work with boxes afterwards (to ship, store etc...) So for the relationships in my database, I will need to work in the box table..
Any other idea?
Well, I copied and paste another portal that works from another form and it works great on my new form...
This is exactly the same settings, formulas etc...
Thanks for helping me anyway!