Error GroundSpeed in Auto mode

I have a problem with groundspeed in my flying wing. I have set a flight speed of 12 m / s, but when I do a mission with auto mode, the speed increases to 22-24 m / s. the altitude that I set at 100m for auto and RTL mode but continues to decrease.

please help me to fix this problem

link flashlog:
Thank You.

Did you solve this problem?