Difference in exception aggregation settings in quality & production environment

Dear Experts,

I am facing a peculiar issue in one of my report. The issue is that when i compare the report in production with that in the development/quality, i can see some difference in the settings of Exception Aggregation for one field. Below screen shots will make things clear:

The above is the screenshot from development and here as you can see that ref-characteristic for the Exception Aggregation is blank or not defined. But the same field in production has different settings

In production i just can't set the reference characteristic to blank. I am not sure that this is even possible but that is present in development. The problem is that the report was changed in production directly and i am trying to restore it to the original version since we were getting some unusual results in the Overall Result field and i suspect that this might be the reason for that.

So request you to explain me the issue and how can i fix this.

Best Regards,

Kush