Zero or even negative pitch during back transition


I am having trouble understanding what is happening during the back transition. In the beginning, the deceleration is decent, but towards the end its speed stabilises at 6m/s until the timeout is reached. The pitch, initially positive, goes down to zero and even a bit below, as if the drone wanted to keep its speed. Does anyone know why this happens? Or could indicate the place in the code where the pitch setpoint is calculated during the back transition?

Weโ€™re using a standard VTOL with Pixhawk Cube, Firmware v1.8.2.

Thank you!