So it is a custom app. ADF & development in general is not in my focus, but I will try to help.
I think you have some problem in your application design.
You can find the query used in that ADF page, and use that query to check whether or not you have a duplicate record there..
If you don't have any duplicates in the primary key columns, then the cause may be a wrong use..
We see this in wrong LOV usages in ADF..
See ->
https://stackoverflow.com/questions/20786404/too-many-objects-match-the-primary-key-oracle-jbo-keyThis may give you some idea.,,
Check this one as well ->
https://udayarocks.wordpress.com/2011/06/04/resolution-to-error-jbo-25013-too-many-objects-match-the-primary-key-oracle-jbo-key