EKF Lane Switch and failed goto

Running ArduCopter with default sim_vehicle commands. Occasionally, the SITL reports:
AP: EKF3 lan switch 0
AP: EKF primary changed: 0

following a command to fly to a point (mode guided) for a while, before it arrives at the point.
At that point, velocity goes to 0, and the drone no longer moves to the goto point.
If I attempt to give it another guided, the command is accepted, but the drone will not move.

Unclear how Im supposed to recover and resume motion to the guided point. Any thoughts?

No clue, and without a .bin log file there is no way to tell.

Good news. After rerunning the scenario, I discovered I missed an event where there was a collision with the ground. Whoops!