I've caught our cat and all neighbors cats as well. Shake the lovin heck out of the cage before you let them out. Have not come back.
The trip is better quick. As it gets more use it will slow down.
It isn't the trip, it's the arm. Or, where it is supposed to hook the door. I will go out in a minute to see if the dog tripped it. If he did, I will get a picture.