Advice on log with crash on takeoff

Hi everyone! I’ve experienced a strange crash immediately after catapult launch.

I have an elevon plane. Lately we updated firmware from 3.9.2 to 3.9.8 because of SB_0000002. At first takeoff with 3.9.8 something happened with pitch controller, plane dropped throttle and did a nosedive for no reason.

Log file attached: crash log

I would highly appreciate any possible advice!

a quick look seems like throttle went to 50% as a response to the airspeed getting > than ARSPD_FBW_MAX

then you can see des.pitch climb steeply while actual pitch drops proportionally opposite of AETR.Elevator going up, not sure why, certainly not stall…

a quick look seems like throttle went to 50% as a response to the airspeed getting > than ARSPD_FBW_MAX

I noticed that too, but I thought that TKOFF_THR_MAX == 100% would prevent such a drop during takeoff phase.

Is there rule of thumb for ARSPD_FBW_MAX param setup (because relations between ARSPD_FBW_MAX, TRIM_ARSPD_CM and THROTTLE_NUDGE are quite complicated, I mean in a way it’s described in parameters documentation)?

About actual pitch… The plane hit the ground at full speed, so it was certainly not stall. I checked servos and elevons after crash and they works just ok.

Thank you for your help!