Studiotek 130 + Wrinkles

I have a 10 year old Stewart Studiotek 130 which has developed wrinkles in the last couple of weeks. It's a tension mount screen, so I'm baffled as to how the wrinkles are there. Is it just the age of the screen, or can heat and humidity cause this? Up until this year, the screen was always in the basement were it's considerably cooler. My upstairs is around 78 degrees (no AC), and humidity is about 40%. I'm in northern Canada and it's normally quite cool and dry here. All of the snaps are in place, and I can't pull the screen any tighter. Any ideas?

Here's are some pictures. The wrinkle at the bottom of the screen extends out about 10 inches.

Thanks for the reply. Batten bar? Is this the frame? I'm not sure what you mean by "downward stop position". I did remove the frame from the wall mounts, but the wrinkles are still there. The only thing that has changed is I moved the screen from the basement to the upstairs about 8 months ago. The screen has been fine up until maybe 2 weeks ago. The wrinkles have been getting worse ever since. I'll try running a humidifier and see what happens. I'll fire off an email to Stewart and see if the hair dryer thing will work.