Problem Solved. for anyone in the future have similar case just perform factory configuration for VOXL Flight Deck by
"voxl-configure-vision-px4 -f" and then re-connect to QGC and you will see the miracle.

@James-Strawson yes,we only test uav in position mode. we didn't use manual for testing.

pls help me soon. we can set up an online support via teamview to make the problem more clearly.

last week it used to work normally. i did't changed any strange thing, just re-configuration the drone to the factory state. by "voxl-configure-vision-px4 -f" to take again the NED position cuz before that i had config vision lib by "voxl-configure-modalai-vl" and the local poistion is lost.

the local NED position is look good at the init state as well as when i move the drone into the other location.

hi, here is the video i just captured https://drive.google.com/file/d/1Am63zD09am8nx_BBpAB2JfTYcf_IFMST/view?usp=sharing

it just is a whitle floor like this

Hello, me again my voxl m500 frame is driff while fly in position mode

here is the voxl/vision-px4.conf text. last time after reset the configuration to the factory -> then i also changed the offboard mode to "off" and the m500 can fly in poistion mode but the performance is not good, it's mean sometime the the driff was maintained. i think the problem is not here. (about reset the vision-config to the factory, i just reset and not config anything...
pls help me!

@Chad-Sweet oh my godness. My mistaken, i didn't realise that before that i had configured UAV off board mode. when I check the /etc/modalai/voxl-vision-px4.conf the offboard_mode ="figure_eight" => so that's why it's cause the problem here. anyway, it's work again, thank you so much for the effective support

Here is the video of flight with position mode, what is the problem ???
video link

every step is correct with the manual document. Here is what we do with the UAV. In the last week i had tested the UAV load in position mode and it's work well, after that i also tried with MavROS node to take-off UAV in Offboard mode. we would set the altitude to take off is 0.5 m but the UAV takeoff higher than 1m much (i had build rosnode after launch).
But it was other problem, in this week we had installed a asus xtion camera and a raspberry pi at the bottom of m500 frame, then trying to maunally filght at position mode but the driff has occurred.