Hi there,
I've run into this a couple times and can't find a reason why this happens.. but i go into an object, create a FSM and put a TRIGGER ENTER on it. Then i do some stuff.. maybe remove it or whatever and then i find that the TRIGGER ENTER option is gone, only EXIT and STAY remain.. i delete the object that i applied the trigger too and the option is still missing. I have had to reload scenes to get the option back. I'm just not sure why this happens.
Thanks!
Caleb