When I flew the VTOL, the ground station showed a malfunction:EKF switch

I found that when switching modes from copter to plane in the air and the tail-thrust motor started working, the mission planner show EKF error and switch the EKF lane. And then just keep switching the EKF lane. the EKF Postion Horiz and compass variance is very high.I tried to start the tail-push motor on the ground, but the error couldn’t come back.

here is the log file