I've had one with the bad tunneling. It was very bad when I first got it, it had been sitting in an unheated garage for quite some time (got it mid winter). I found it cleared up slightly after being in the house for a while. It wasn't completely fixed but it was not nearly as bad as when I first got it.

The other two I had did not have that issue. However, it seems over time one of them did develop tunneling(I sold the screen to Brooklyn).

Would be good to get to the bottom of the issue and figure out if there is a way to reverse it, or at least prevent it on ones that have yet to develop tunneling. Since it seems age is going to take out more and more of those screens.