No altitude limit. Again, the solo never tried to return to home. I just saw that the icon was red, and scooted backward several feet. I went forward again, lost signal again, and brought the helicopter back toward me so it WOULDN'T RTH and hit something.
I thinks it's just a shortcoming in the solo's hardware. I'm gonna get better antennae like Adimuzio suggested. If the solo has poor connectivity, the antennae seem like an apt solution.
By comparison, my ancient Phantom 2 Vision--non +--has been in cities, sprawling suburbs, and all kinds of other high wi-fi areas. I've lost GPS plenty of times, but the controller/helicopter connection has always been terrific.
I think my p2 has a sort of bug or something too I've had no gps issues myself but have had two instances where my connection to it dropped and it headed off on its own and these weren't at longer distance than I've had solo, I ran toward it and got it back but it wasn't headed home. It's only been twice and I've had better than a hundred flights on it but these issues played a part in me buying solo so I could fly without worry as long as I did everything right on my end with the warranty.
I've also not had to survey areas for wifi or be worried so much about flying near just about anything so I totally agree something is odd with solo and it's likely hardware related, but you'll really enjoy the antenna upgrade at least I have in the areas I've been so far.