Hello. There are a couple of issues on take off:
1- right from the start the aircraft tries to achieve the reference heading, which is the heading it had when the battery is connected and turned on. If the aircraft is later moved to a takeoff spot and the heading is changed it will try to rotate to the original heading as it is taking off which can make some motors spin too fast and cause a flip.
One solution to this would be to add a command to the takeoff block in the flightplan so that the heading is reset. I could not find which command can do this.
2- if the throttle is set to 0 in the RC for some time after entering the takeoff block, it is possible that due to GPS fluctuations the CLIMB point will no longer be located directly above the current position of the aircraft. From the start the aircraft tries to move horizontally to come back to the CLIMB point. This causes it to try to take off with some pitch and roll which can cause a flip.
This could be avoided if the throttle is increased immediately after entering the takeoff block, but there would have to be a big warning somewhere for users to be careful.
There is another problem, with altitude, when the throttle is not increased immediately. This is described in detail in my previous email with subject "problem with rotorcraft vertical guidance".