The first flight was normal, but after the second takeoff, it kept climbing and could not descend
Post a .bin log, I opened your log here and have no data to analyze.
@Wade-Hong Looks like you are using very out-dated firmware (Copter 3.5.8). What is the flight controller? any reason that you haven’t upgraded your firmware?
It appears that you had disarmed the aircraft inflight? Why didn’t you switch to stabilize mode?
After looking at your data, It looks like there was a problem with the EKF and its estimation of climb rate and altitude. I’m not sure that I can be of any more help than that. The innovations for both vertical velocity and position are positive and growing. You can read more about this here
This describes how the current firmware handles high vibrations which cause undesirable innovations and bad altitude estimates. I don’t believe this was how the failsafe works with your version of firmware.
I use the RadioLink Mini PIX flight controller, regret using him
CubePilot will be installed on 900-E1 in the future, it should be able to solve the vibration problem
Well you can still have this problem even with a cubepilot. It depends on how well you have balanced the rotor system and how well you have the flight controller mounted.