I too have had this happen. 5th flight. Scared me for 52 seconds as it accelerated in increasingly wide arcs until it made a sudden move and struck a rock at 50 mph.
3rd flight of the day. Previous flights totally perfect. 16 satellites, full strength...
I did a lot of research and I have a theory: the Kp-index.
K-index - Wikipedia, the free encyclopedia
I checked when I arrived. A cool 2. At 3 pm when my bird went insane, it hit 5.
I theorize the quality of signal degrades in some way and the gps brain can't be trusted under these magnetic storms. I theorize specifically a Kp-index of 5 can be very bad.
Only a theory. Definitely lots of moving parts and software to blame as well, but I definitely believe I'll fly in Atti mode a lot.
Bennino