Thank you for your post.
I have several files with multiple keys (some with 2, some with 3, but none with 4). In each occurrence, I'm able to add a record to the child table when no information appears in the portal once all key fields are entered.
I created a new database with two tables having four key fields (aptly named field1, field2, field3, field4), and I'm able to add without a problem. I know you said this worked fine with a small set of records, so could you provide me the number of records in your tables? I'd like to try and duplicate the problem and see if there is a problem within FileMaker Pro.
There will be an identical response to your post in the bug section.
If your system works on a small amount of data but fails on on a large set then I would suspect that the way your larger data set is handled is the issue, check the way your child data is created & double check if the info in your relationship combined key in all new records to be processed are consistant.
I am guessing you will find that there is some data missing from your relationship combined key field therefore a relationship is not being made.
It only takes one bit one bit of info in your relationship field to be different to cause an issue, check spcecifically for spaces at the end of your relationship fields for each record (sometimes users accidentaly add extra spaces that are not always easily visable).
A nice quick check method would be to use a calc field Length(relationship field) to compare relationship key against new data relationship key data side by side on the same layout. Ones that dont have the same number will your problem data records.
Any system will always handle the data the same way irrespective of ammount of data if no design changes are made to the system.
Let us know how you get on