[snarkpup]

Sounds like the same trap I have. I used tuna, and it seems the cat would be able to get the tuna and exit before gravity could completely close the doors.

This is one problem I never experienced. Unless you have actually seen the cat dart out while the boom is being lowered, I doubt this is your problem. You may have something like problem #2, or perhaps the bait is being taken by an animal (dog, possum) large enough to block the fall of the door and then back out.

[ASA Vet]

I haven't seen the tripper, but it isn't a dog, as the yard is fenced. I have caught possum, and racoon. Hope to not catch the friendly neighborhood skunk.