My experience with duplicate metric delivery was coming from the same platform. Although CM360 and DV360 can have the same tracked metrics, the first thing I would check is if this Ad Account is added by multiple Supermetrics users. It took a long time to figure this out unless you are querying the most unique key to determine this in BQ.

Hi ​@somesh, 

Thanks for sharing this.  In this case, we recommend that you double check that you have not selected the same account twice.
Also please note that with Google Campaign Manager 360, you can select account on partner level and advertiser level. If you’ve selected both, then the results will double. Please select an account only on partner level OR advertiser level.

Let me know if this helps or not. If not I’ll ask our Support team to take a look