It does seem there is kind of a Bug here, but maybe I got it wrong. I Did try some testing on the Forms Data Grid, it seemed like the Added Row only gets registered when there is a click on Add Another button after the Entry else it doesn’t get added to the Datatable.
After Clicking on Submit, and Checking the Debug will see that the Last row is not updated (For now, after the Last Row Entry we would need to click on Add Another and then Click on Submit) :