The larger agricultural drones are also amazingly impressive, those I've seen up close doing real work and they are so reliable it is almost boring.
I wonder what the reason is that yours behaves the way it does, that sounds like a real challenge to find out though with the closed system like that.
Drones that rely on GPS are very iffy as soon as the GPS fails, I've seen more than one inexplicable 'fly-away' happen. I've found a really neat trick to test drones that are not 'known good': just find yourself a long stretch of really light chain and tie it to the drone. As long as it behaves: no problem. But if it tries to take off by itself at some point the length of chain weighs more than the drone can handle and it will stop ascending. That way at least you have some kind of safety measure that does not immediately impact the drone in a material way as long as it is near to you.