I have the following suggestions that started off as a couple and spurred other ideas:
1. I am still thinking that this could be a protein extraction issue. It is really hard to get good protein extraction by hand. But, if that is the only option, I think I would push your mixing time to a solid 20 minutes. It should be REALLY sticky.
Another thought is that I am not sure that you have enough fat. The more I think about it, this may be more of a primary factor. I typically use a combination of venison and 80/20 beef along with my pork butts and run my mixture 50/50 to do my best to get 20% fat ratio. With less than 1/3 of pork and the lean 90/10 burger, I am not sure that you have the recommended 20% fat in your meat block. Without enough fat, protein extraction will be even harder to achieve.
When I do my SS, I will occasionally get "some" wrinkles, but the casings are tight to the meat, whereas your's look like they are kind of loose, which again points to lack of protein extraction.
2. I think I would ditch the jerky dryer. I don't think that you need to add any extra moisture in the way of a water pan or anything. But, I am not sure that the jerky dryer is necessary.
3. Make sure that you have these chubs up as high as you can in the smoker as this is where the temps are most stable, hopefully to the point where there is only an inch or two to the top of your smoker. I am not sure about your #2, but I have to rotate mine about halfway through because the rear of my #3 is quite a bit hotter than the front. So, I rotate them to maintain even temperature.
4. After your ice bath, I would hang the chubs in room temperature for a good 1-2 hours before putting them in the fridge or out in the cold again. This will help set your casings before you start cooling them off further.
5. If 1-4 don't resolve the issue, I think I would try to smoke a little hotter which should result in a shorter smoke time. I have a feeling that up to 12 hours is way too long and you are cooking your fat out of the chubs. This may or may not be the case though, since I think you are a little low on fat ratio to begin with.
I think I would use something similar to the following schedule:
150F for 1 hour
175F for 2 hours
200F until internal meat temp of 154-160F