Keep in mind TIP is still improving, and the product still isn't close to the original Polaroid, though it is good, and is a lot of fun.
There is a little debris on my rollers, and it has not caused any artifacts in my photos. Results are very good if I set the dial half-way to full darken, and take the picture in full shade. I've never had the mottling.
In the past I have had problems with the chemicals not spreading completely, but those were the first Impossible runs, and I'd had the packs for about six months before using them. I've learned to buy from a source that has fresh film, and use it within a couple months of receiving them. No issues when I do this.
I think you may have a combination of problems. Near the bottom of your photo almost looks like a light leak - have you had it on each photo?. The mottling may be the emulsion or dirty rollers.
I brought 3 packs of the color to Hocking Hills, and the first two ejected the dark slide, but the film would not come out. I "fixed" the first without a dark bag, outside. I had to slide the film toward the bottom of the pack so the ejection finger could grab it and push it out. It was fine after that, but I have fogging around the edges, similar to the bottom of your example. The second pack I did in a changing bag (since I had a clue on how to fix it) and it was fine. The third had no problems. I'm pretty sure it's not the camera.
We went horse-back riding yesterday, and I gave a couple instants to a couple people who were riding with us. The photos were in complete shade (under a canopy of trees) and came out nicely; our fellow riders seemed to enjoy them. In direct sunlight, they would wash out and have extreme contrast.
We're in a little cabin in the Hocking Hills region (we're in Logan, Ohio), so I don't have a scanner at the moment. If I can get a decent phone-pic of one of the photos I'll try to upload it later.