I have the same equipment (stock p2v+ / Galaxy S5), and had the same problems.
Success after the following steps, (works as expected):
1. My home is located at the edge of restricted airspace. The DJI equipment prevented Ground Station from working at my home (symptoms as you described).
2. At another flying field, with no airspace restrictions, I connected all equipment (as normal). On the Galaxy S5:
2.1 WiFi enabled (obviously).
2.2 Mobile Data checked. (Internet connection to d/l maps)
2.3 Location enabled. (To get map centered on THIS area)
2.4 Swipe to Ground Station, gesture zoom as necessary, cache map.
2.5 Turn off Location. (Prevents further map d/l activity) ... Maybe unchecking Mobile Data would be useful at this point(?)
2.6 Input flight plan: speed, waypoints, altitude, location.
2.7 Review flight plan ("Done").
3. Everything ready to launch flight plan (just hit "Go").
So two things created issues:
1. MUST be in unrestricted airspace!
2. Toggling "Location" (or maybe even better, uncheck "Mobile Data," didn't try that!), was necessary to keep from reloading map (possibly interfering with WiFi connection to Phantom).
I have run several successful Ground Station Missions with this method / equipment. A nice feature: The flight plan can be re-run, it remains until theDJI Vision / Ground Station app is closed, so it could be tweaked if desired. A downside is that a flight plan can not be created at home, later loaded or implemented at the flying field. I COULD load high level maps, zoom NEAR the flying field, but I could not zoom to a level sufficient for adding the waypoints, it automatically flips to the Phantom Connection Broken Screen, and will return to the max zoomed out screen.
Good Luck!
-Dale-