When you tap the Load Plan button in the native app, Dronelink creates a new Mission and places a copy of the Plan inside of the Mission. This lets you run that Mission to completion without worrying about the Plan changing during flight (because it has a copy). If you do update the Plan while the mission is still in progress (not finished, not aborted, but either running or paused), the Mission will be unaffected. If you want to fly with the latest changes, your choices are to either finish the Mission, or abort the Mission. As long as there is an in-progress mission for a given Plan, the native app hides the Plan itself because it is considered unsafe to have multiple, in-progress Missions for the same Plan. Once you finish or abort the Mission, the native app will let you load the Plan again as a new mission with the latest changes.
If you create a Mission from a function and want to fly that Mission again, you can find the Mission in your Mission history tab for your account and copy the Plan into one of your repositories for later use.