It is NOT unusual to lose GPS - any number of things can do it.
It's very, very unusual to lose GPS in flight.
To lose GPS you either have to:
- Fly under cover or terrain that blocks the skyview or
- Have a faulty GPS receiver or loose connection or
- Mess up your compass by launching from steel or reinforced concrete which forces the drone into atti mode - but in this case, you are probably going to have other more serious control issues as well.
Avoid those and you should never lose GPS in flight.
Heck I lost GPS in my driveway and had my Mavic plow into a tree. So let's dispense with that assertion right away.
See #3 above NEVER launch from or land on reinforced concrete. It's just asking for trouble.
I've also lost it under a bridge and as I stated plainly - while walking between two new towers (about 600 and 800 ft tall)
See #1 above.
Fly in locations like that and you need to be prepared to lose GPS. That's the chance you take.
RTH works with lost signal as long as it has GPS.
Lose GPS and what do you have? Nothing except likely a flyaway - which I'm sure you've noticed happens more than a few times.
Lose GPS and your Phantom doesn't fly away.
It just hovers and is stil fully controllable but subject to drifting on the wind.
If you don't have the situational awareness to deal with that, it comes under the category of operator error.
But as I said above, it's extremely unlikely you will ever lose GPS in flight.
Truth is satellites come and go as they traverse their geosynchronous orbits and sometimes you just lose the numbers and thus can't get a lock on location.
Truth is that if your Phantom has a good skyview, you'll always have plenty more sats than you need for position data.
You should never lose GPS when you are flying with a good skyview.