Issues about autonomous landing for drone

I’m doing indoor vision-based landing. The simulation in gazebo works fine. However, in the real world, the drone has detected the target(which is a QR code) successfully and try to decrease its height as well as adjust its x and y position, then, when the height is low enough to land, the program switch from the OFFBOARD mode to the LAND mode, however, it suddenly return to the initial takeoff position, rather than land on the target.
I have no idea what may trigger the drone goes back to the original place.
Here is my flight log: Flight Review (

Thank you in advance for your help.