Can't change mode in flight?

I flight sky suffer X8,yesterday for the first time with pixhawk ,I transfer to autotune mode after take off above 150M hight .the plane suddenly climb in 90 degrees several seconds then become nose down ,I transfer back to manual mode immediately and keep flight in order to find out what happen to to flight controller,I try to transfer to the autotune mode again after climb up to about 200 hight ,but the plane keep nose up in 90 degrees then become nose down again,so I try to transfer back to the manual mode ,but the plane didn’t come back to manual mode ,and the plane crash!
I analyse the Tlog and dataflash log ,and find out that it’s because pitch servo out reverse.but the question is that why I can’t change back to manual ? I found the RSSI is OK in the data flash log,and the telemetry control signal is OK ,the plane is away from me just about 500M
Do anyone have any suggestion to analysis this accident ?
by the way the channel 5 is mode change and it works good in the ground .

Immediate pitch up and down commands often lead to very high accelerations and forces including structural damage and physical equipment breaking. For example, the battery may come loose, breaking the receiver input wire. If you post a log, we can take a look at your receiver’s input to see the integrity of the system.,The above is dataflash LOG log; the above link is the TLOG