"[lpe] vision position fault problem & INAV mode

Hi everyone.
I was used pixhawk 1 with PX4 firmware 1.4.4 version in INAV mode and it works well.
But as you know, pixhawk 2.1 published and I want to use it.
When I installed firmware 1.4.4 to pixhawk 2.1, sensor calibration mode in QGroundControl was not work!
Then I installed firmware 1.6.3(px4fmu-v2_lpe.px4) and sensor calibration mode was workd. But at this time INAV mode was not appear! Is the INAV mode is disappeard in new firmware version?
After that, I tried to use LPE mode instead, and I found that [lpe] vision position fault message and [lpe] vision position ok messages were poped up for few minute even if mavros/vision_pose topic was pubilshed continuosly in 40Hz. After few minute, [lpe] vision position fault message did not come out and mavros/local_pose value gives correct value.
Would you let me know why “[lpe]vision posiion fault message” occures and how can I solve it?

Thank you for reading and I appology for bed grammer… I hope you understand my question and you could help me.