Your motors are bottoming out.
Here, you can see that the drone is not achieving the target climb rate, and your motors are at minimum throttle. Basically what’s happening is that the attitude controller is saturating the altitude controller; it’s the opposite problem I explained in this thread, if you want more information.
There’s a few things you can do.
- Lower MOT_SPIN_MIN. It needs to be greater or equal to MOT_SPIN_ARM, but you can lower that also, it just needs to be high enough that your motors spin up reliably when arming. This will increase the throttle range on the bottom end.
- Lower ATC_MOT_THR_MIX_MAX. This parameter decides the priority of attitude vs. altitude control when they can’t both be controlled perfectly. It is rare to need to lower this, but you may find it acceptable.
- Change powertrain or increase (battery) weight. If the above software changes aren’t enough, you might just need to change hardware. Increasing battery weight is a not-terrible way of doing this without killing your flight time.