RTL stalls on climb

Hi,

Have the APM 2.6 in a bix3.
On RTL it flies fast and more steep up than possible in FBWA. Yesterday it caused 2 stalls just after each other.
What parameters controls RTL flight?

One more comment in FBWA I normally don’t see stalls. Seen full rudder stalls. But even when gliding unpowered full elevator will not stall plane.

Here are data from the dataflash logs. It seems to have a hard time keeping the 20 degrees up, and in center of graph it dips to nose below 0 twice, and a few more where it keep positive attitude. It clearly is not doing much to prevent stall here.
Also wonder about slow GPS speed, wind speed this day was 3-7 m/s at ground.

Any setting to change to avoid it next time ?