There is nothing hypothetical about KP index. You do know how its measured right? By using ground based magnetometers, just like the one in your phantom. Its an actual measurement of compass errors due to -mostly- solar activity. You can argue over at what level it affects our drones, but when it hits 9 or 10, I assure you its not a mythical thing.
As for losing GPS; that also most definitely happens, its happened to me plenty of times, and not just when flying without clear view of the sky. GPS signals are radio signals and can suffer from radio interference; either from ground based sources or ionization of the upper atmosphere. They are also influenced by thick clouds.
The KP-index affecting your flying is a much hyped myth with no evidence that it has ever caused any problem.
The commonly held belief is that at KP-index of 5 or above, the sky will fall and your Phantom will fly away, etc, etc.
But no-one has ever come up with any evidence of problems caused by flying with a high K-index.
The general idea is that it will affect GPS accuracy, because high K-index conditions do have an actual small impact on GPS accuracy.
But just how much and what impact does it have?
Here's something to look into:
http://www.nstb.tc.faa.gov/reports/PAN86_0714.pdf
Look at P31-32 and you find that GPS errors were measured at a couple of metres.
But GPS already has an error of a metre or three anyway anad you don't even notice that when flying.
If you flew with a slightly larger GPS error what impact would that have?
Probably nothing you'd ever notice.
By the time KP-index is high enough to cause .
GPS signals are radio signals and can suffer from radio interference; either from ground based sources or ionization of the upper atmosphere. They are also influenced by thick clouds.
GPS affected by clouds? Really!!!
You've just given your credibility away.