I agree it could be the surface your mat is on. Weird but it does matter. One mat at our sew group no one could cut on, skipped cuts, awful. We moved the mat to a different table surface and there was no problem with the cuts. We still don't know why. I have a rotary cutter that won't cut fabric, even with a new blade. I keep it in my quilting supplies to show others at classes. They can't believe it. Some even put new blade of their own in it. Still doesn't cut. ?????

Yes, this has happened to me at a quilt shop when the mat was on a plastic folding table. Those surfaces are not always flat.

Soaking it should help, I think the drying out theory might be right! Hope it works for you!

Have you tried turning the mat over and using the other side?

I have cleaned mine but never knew to soak it thanks for the tip. Only been 12 years. LOL.

I love my Olfa mat. I have two. One I've had from the beginning and it is about 20 years old. The other I got from a friend who used it a lot and it probably is at least 20 years old as well. That one is a large one. I've never had any problems with either. My hunch is it could be the surface that you have it on. If it is a large one and there is a bow or uneven surface it might affect the cutting. I always make sure I have a good solid surface to put them on. I had a Fiskars mat as well a few years ago and it warped in the first year I had it even though I stored it properly and kept it out of sun etc. If I ever got another mat I'd get an Olfa given the good service they've given me.