When GPS glitch happens vehicle(quad copter) goes to the RTL flight mode. Ideally , if glitch happens vehicle must be in ALT hold or LAND mode. We are using arducopter 3.6.9 firmware with Pixhawk4.
Steps to produce :
Remove propellers
2.Connect quadcopter to mission planner
3.Give takeoff command
4.Take into shade where GPS sat count is less where GPS glitch will happen
5.After 10 to 15 seconds quadcopter goes to RTL mode instead of LAND or ALT HOLD
Your GPS glitch is severe enough to put position outside your fence and initiate Fence breach failsafe (which is RTL) but does not occur long enough to initate EKF failsafe (which will land)