This could be simply the leather stretching or, more seriously, a broken/ damag d tree.
This can be checked by a saddle fitter- for most accurate results.
There will probably be a video on YouTube to show riders how to check.
I hope more people thought about the answers than commented - because getting it checked for a broken tree asap and not using it in the meantime if in any doubt was it!
Other things to check: stitching, even flocking, that both panels are the same thickness (esp if Cair panels).
Real life experience (not my horse) prompted this thread!
I have a saddle which developed wrinkles in the seat which I did know was possibly a sign of a broken tree. I've had it from new and it hasn't been dropped or anything. A saddle fitter has checked it and says it's OK, possibly due to my partner having a bony bum as it only went like this when he started using it!!
My husband’s horse’s saddle has gone wrinkly too and it’s definitely not because he has a bony bum. Saddler didn’t seem to be able to offer any explanation as to why it had happened. It has definitely not been dropped.
Different materials will wrinkle differently, thicker softer foam and thinner leathers will wrinkle the most. Then if you have a driving or otherwise overactive seat you'll be much more likely to stretch it which is what causes the wrinkling.
Safety checks should be done at least weekly and more often if you discover something that might be beginning to go. Stirrup leathers and girth straps (and of course your girth itself!) are the most crucial. Checking the flocking is a good one but most people don't know how to do it correctly, get your fitter to show you. Leather is a natural material, flocking too, and if you don't use enough pressure with the part of your hand that allows you to effectively feel what the horse feels once there is weight in the saddle it can be easy to have a heart attack about apparent irregularities.
Yes air panels should be checked regularly for correct inflation or leaks. And it's never a bad idea to feel what your horse feels, checking the underside of pads (especially sheepskin which can hide sharp seeds, thorns etc) and feeling under the saddle on the horse, again ask your fitter to show you.
It's very interesting to learn what else would cause a seat to wrinkle, my first thought would be damage to a tree but I have known saddles that have developed wrinkles on the seat and on checking the tree has been sound.
Automatic saddle check for me every ride are stirrup leathers, girth straps and girth, both stitching and condition of both. Also check for earwigs! They have a habit of going under saddle flap overnight and I don't enjoy them crawling out on me! Always shake numnah out or give quick brush over. None of it particularly takes up time it's an automatic check as I'm tacking up.
Regular saddle checks is check flocking for unevenness and saddle generally for symmetry and fit.