Looking at your pictures, I'm thinking you are right. Squirrels getting away. The loops look too big to me. I use a 1 inch thick running pole between two tree's like Northof50 mentioned about Trapper Ron's squirrel posts. I use a very small circle, about 1 1/4 across or diameter. If they are one a skinny running pole, and the snare is about 1-1 1/2 inches above the pole, they should be centered and get caught.
If you can, add a couple of skinny running poles between two trees, with about 6 or more snares on it. I think you will start catching more squirrels. I see (you picture) with the thick tree support pole, it leaves them too much room around the snare. I also think you should tighten up those snares on your running pole, they are loose, use pliers, it will help get the snare set before they move it around on the pole. Just a little more attention to detail and I think you will be happy. If you put them all at 3 oclock, tight to the pole, it pulls them onto that side and they usually jump from the side you tied it on. Tighten them up so the snare won't move.
Does not look like humans messed with it from the pictures, Thanks, much easier to help you. I don't like the pole on the ground, that would be harder to snare them. Horizontal skinny pole is what you want. Nothing touching the ground.
One trick that works up here is a red mechanic's rag. I put one in the middle of a running pole, 4-6 snare on each side and lure on the rag. They red color seems to be the attraction along with the lure. They will shred the rag if they make it through the snares. It's pure white in the winter, so the red really stands out in Alaska. Might work down there too. I get 2-3 on a pole that way in one check. Good luck, hope you start hammering them.