Originally Posted by caspharm

Do your rulers get direct sunlight for a good part of the day? You have all those lovely windows and the sunlight might cause the warping. Or do you have a bow in your cutting table, since there is no support under the middle of it? Those long plastic extrusion tables can flex when you apply pressure on them.

I know I have to be careful when cutting on a part of my large cutting mat, since it is curved from being rolled up for a long time before being placed on my cutting table - made from a dining room table.

I don't think the pegboard would cause the problem.

As WishIWas Quilting said, it might be the fireplace as well. I agree change the location of the pegboard if possible.