Hi Kevin,
in normal case there should be never such glitch. It should do just what is programmed.
It is hard to say without very carefull examination of all the settings in the unit.
But we can exclude all possibilities step by step. It looks like something being mixed in the radio that is doing such unexpected thing.
It could be for example a channel value that is used for Bank Switching - this value can be very, very close on the edge where for example Bank 0 is activated, but if a channel drifts little bit it will happen to be at Bank 1. Channel drifting could occur on its own over time. It could be also theoretically faulty switch.
But as you said, to activate the Rescue it is necessary to activate Bank 1 and then momentary button. There it is very dependent on how it is programmed in your radio. If these two things are needed, then I guess that it is not caused by faulty switch.
If some mixes are used, then there could be a situation which will trigger the rescue incorrectly. To verify if this is the case, you can simply try to put all the switched to the same position it was during the accident and verify if there is no point which can trigger the rescue on the ground - because in the flight it will do the same thing.
Lastly it could be also caused by for example a servo arm or a push rod that went away - maybe during some pre-flight check. If for example one of 3 servos is not reacting, then as result the model can uncontrollably go up. If this was the case, then after "landing" it should be visible that something was not in position (servo arm/push rod).
The same thing could occur if some cyclic servo will die.
All in all, if it was transmitter configuration problem, the problem should be reproducible on the ground. If it was a mechanical issue, you can find in your memory if something odd happened.
I think that these are the most probable scenarios that could explain the issue. Important is to find it, otherwise it will very likely happen again
Can you also tell me what receiver connection you are using? You can share your settings.