Ardupilot 4.3 failsafe trigged, drone bounce with zero throtle


i just built a 3.5 inch drone with Holybro Kakute H7 Mini v1.3, flash ardupilot 4.3.1 firmware, for several days it fly ok. But today, this 3.5 inch drone fly indoor triggered radio failsafe when landing with unknown reason.Attached the log file,
14 1970-1-1 (505.7 KB)

I fly in stablize mode, when landing, I low the throttle to zero, the log files shows ch3_input is zero, but ch3_out is bouncing, which cause the drone bounce on the floor, then the drone loose control and crash.

what problem cause the drone crazy bouncing, please help