I’ve done loads over water - long distance too - never seen it make any difference!
Which is rather good - since they were Litchi flights and it would have tried to maintain the height on the display.
I always do it this way. I’ve normally got GPS as soon as the remote connects
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It’s certainly a logical approach … tho (even when not in a serious hurry to catch a shot) I usually do phone, RC, MP.
The reason is that my “dedicated” drone-phone is also a backup phone and takes a while to boot and complete all the background crap before it can give full attention to Go4.
Then I switch on the RC which triggers the choice of app on the phone to be used : Go4, Litchi, and something else I can’t recall atm (because it’s the first two that are the main ones I use).
Then the MP - because I always want maximum flight time available - but I very rarely take off before it’s confirmed the Home Point … which is when it has GPS location (either by the spoken “Your Home Point has been set …”, or the double green flash), and by confirming either/both with the app saying the MP is in GPS mode.
Edit: Also - on cold days - I don’t want it sat with the batteries getting cold. The quicker it’s in the air, the sooner the battery drain is keeping them warmer than sat on the ground doing nothing.
That’s the same with the Air - no GPS restricts height to 30ft until you get the GPS lock. Also remember that it’s not until you get a GPS lock that it sets the RTH point, which would have been over the water!!
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Unless it’s in a more recent firmware than the one I’m using on the MP - that’s definitely a difference.
Might be to do with the Mavic Air rather than the app - had it happen to me this afternoon. Won’t go higher than 10 feet when you start until in OPTI mode - and tellls you that you are at maximum altitude.
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I’d imagine that’s the drone firmware, not the app.
Easy to check - fly with just the RC.
If reverting was easy, I’d quite like to bring mine up to date for a while.
Perhaps s/h ones will get cheap enough for me to have two? 
In the interest of the pursuit of knowledge, of course 
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I thought RTH was set as controller location?
Nope.
It sets Home Point to the drone location when it first gets a GPS fix … and the green lights do a double flash.
It then sets it again when it takes off - in case it’s been moved.
You can also re-set it from the app to where you are.
I’ve used that last one a lot when trekking whilst flying … otherwise it goes back to where it took off.
Also imperative when flying from a moving boat.
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Wait for GPS to remove height restriction limits… check that firmware did not reinstate child lock!.. Turn off flight modes and turn beginner mode on.
I shot off the ground after the first M2P update. I intended to head up and over some trees not realising that beginner mode had reinstated following update. Suddenly the flight altitude held just as I thought I was to clear the trees and I shot into the trees instead of over them. Luckily, I just stopped just shy or I’d have done some damage. DJI really need to stop this from occurring!
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One thing I heard somewhere if flying over water the drone has difficulty getting a fix on height as it all looks the same, this would be further compounded if it is dark. So that combined with the fact you had no GPS may account for what happened.
Just a thought.
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All I can say to that is “Don’t believe everything your hear.”
During flight, height has absolutely NOTHING to do with the nature of the surface you are flying over!
It’s TOTALLY controlled by the IMU and barometer.
GPS isn’t used, either, because GPS height is unreliable.
Fly your Mavic … at constant height … over water, even … and look at the detailed logs.
These will show barometric height very close to constant, and GPS height varying.
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Ok guys, this solves it and thanks for the info!
Lack of GPS LIMITED THE HEIGHT it would also account for the height wobble a bit. Then I got a lock and RTH is indeed over the sea (cheers Brian).
I was freaking out at the time but log shows all the messages I missed!6FCF0BED-AAF9-4959-AE93-CB90F6A2A14F.MP4 (6.2 MB)
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@OzoneVibe
Thanks for your correction, I don’t always believe everything I hear, but it did sort of sound plauseable.
I haven’t looked much at flight logs. which site is best for reading the flight logs from my MP?
Oh and great to hear about the CAA recognition.
https://www.phantomhelp.com/logviewer/upload/
Despite the name of the site - it works for other DJI drones other then M2 … unless they fixed that recently.
@OzoneVibe
Thanks for that, you should get a badge for being the member that has helped me the most, you would certainly be my nomination for “Best Drone Mentor”
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Don’t give him any ideas 
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