This may be an old bug that has been fixed. I understood that if you had DJI running in the background on your iPad that it would conflict with DD. To prevent this you would only run one or the other.
This presents the problem of shutting down DD during battery changes so I can check the bird with DJI before continuing the mission. Sometimes on restart, in poor cell coverage areas, the app just spins upon restart. Not sure if this is an iPad Mini problem or if it is an app bug.