Does ForeFlight Mobile need to be running to receive ADS-B data?

Yes, in order for ForeFlight Mobile to receive and save weather and NOTAM data from Stratus, it must be running. If the iPad/iPhone screen is turned off using the sleep/wake button on the top of the device, ForeFlight Mobile will no longer receive ADS-B data. ForeFlight Mobile must be shown on the device screen to be able to receive data, but screen brightness can be turned down to save battery.