Definitely raccoons. Not that they're "smarter than" people, but very wily, very handy, and very persistent.
Now that they've solved your trap, you may need to use another model--or change something about the one you have.
Raccoons can open latches just like people can. I don't know if the story is currently findable on Search, but two friends of mine here in the Bay Area lost protected pets to raccoons a few years apart. One, a snail-hunting duck, was wrested from her locksmith-approved nightly shelter by raccoons and killed; the other, a bunny, also in an approved hutch for overnight shelter (owner is asthmatic), was similarly attacked and killed.
In both cases, the latches were "raccoon-proof," according to local locksmith ratings. There was some local flap about the meaning of "raccoon-proof," and now double-locking, *with* padlock, is the only way around here to protect certain animals who must live outdoors (e.g., chickens, ducks, kids, lambs). That or an outdoor dog 60 lb or greater, and many Bay Area dog-lovers won't keep Fido outdoors: Fido wants to be with The People, and The People want Fido indoors with them.
So padlocks and double-walled chicken enclosures, etc., it is.
BTW, you do not
want to see the results of a smaller dog vs.
raccoon fight. The dog must
have a significant weight advantage over the raccoon and
a strong protective drive for "its" flock to go up against a raccoon. I myself had to drive off raccoons from our yard in Berkeley in the '80s and '90s when we had only cats--it took the JET setting on the hose, with significant water pressure, carefully aimed at either the tip of the raccoon's nose or precisely under its tail to persuade the larger ones, approx. 26 to 30 lb, to LEAVE NOW. Smaller ones left after a water shot to the flank.
Ya got raccoons; sorry.
Sunset Zone 17, USDA Zone 9