LPE vision position fault problem

Hi everyone.
I am trying to giving motion capture position to pixhawk 2.1 vis using topic “mavros/vision_pose/pose”, but sometimes [lpe] vision position fault message comes out and z position value of “mavros/local_position/pose” shows very different position.
LPE_FUSION paramter was 12 which only allow vision position and yaw.
I want to geet [lpe] vision position ok message all the time when I power on Pixhawk 2.1… .What is the problem?

And one more thing… previosuly, I used pixhawk 1 with INAV mode… Could I use Pixhawk 2.1 with INAV mode? Because recent firmware does not give INAV mode, I can not use it.

Thank you