Altitude dropping when Auto mode

Hi Guys, I’ve built a heavy-lift quadcopter. It flies well in stabilize, altitude hold, and loiter mode.
but when it flies in auto mode, the copter loss the altitude. starting with 3m height at take-off and then start dropping to about 1-2 meters, and then come back again to 3 meters height when the copter back to home position.

here is the baro and gps.alt graph

anyone knows how to fix this ?

thank you.

I have the same problem. Has it been resolved?