So you didn't switch to P mode as well?
That should have solved it. In fact you should have tested that switch before sending it on its first Litchi mission.
Updating the firmware right before trying out a new third party app is not the way. You should have tested the update first before trying anything new. Not that it is definitely firmware related but you want to be absolutely sure it functions 100%. I always conduct flight tests after any firmware update. You can even check everything on the simulator first (the I2 also has a sim doesn't it?), including the switching to RTH, F,P and Atti modes. If Go or the firmware would be screwed you would notice it even before you take it into the field..
Good that you managed to stay cool and save the situation. Next time I suggest you use the P/F switch to get out of autonomy when anything happens, and always do test procedures like I mentioned above and you will be fine for the future.
There is no "F" switch on an Inspire 2 remote. All the 3rd party apps work in "P" mode.