Here is a video explaing how to best cache the maps, simply going into google maps and using "okmap" , wont save to the app unless you currently in the app. If that makes sense. Best to escape (while running) out of app reconnect to wifi hotspot or phone LTE service, zoom into the area you'll be flying. Then return to the app.
Also kenargo who has written the DJI ultimate flight app is currently has a working Save Missions feature as well as other cool features available on Google play. http://www.kenargo.com/AndroidApps/UltimateFlight/about.html
(NOTE: I cannot verify if it works on all versions of the Vision)
See this thread