Pitch up and underspeed detection

I am flying customized plane using PX4 firmware. During the flight, underspeed is detected twice; once during takeoff while another during level flight. The underspeed detected during level flight happens just after the plane pitched up. Once this underspeed is detected; plane couldn’t recover from stalling and crashflight log file as opposed to TECS uncommanded descend recovery algorithm. The log is attached and graph is shown below.

Pitch Graph

Airspeed Graph

Throttle Graph

The log link is