When you duplicate an Interactive Grid in APEX, if that region has a process to perform Automatic Row Processing DML; the new, duplicated region, will not have a DML process created for it.
You can create a DML process for the new region from scratch or duplicate that of the original Interactive Grid and then update the Editable Region property of the new process to the name of the new Interactive Grid.
I’ve created a simple example app that shows the results.
The scripts for the app and underling tables can be found here.
It’s debatable if this is an intended feature or a bug, but the duplicate feature works this way up through APEX version 24.2.10.
I hope this helps. While there is a simple resolution, it can still be surprising when it happens if you don’t remember and your new IG mysteriously doesn’t work like the others.