When I use my mat on my kitchen peninsula & stand on the long side, I have cutting issues. Discovered it works better if I stand on the short side so I believe there is a slight dip in the countertop.

Invest in a Stripology ruler and be sure that your fabric is folded carefully.

I also love the stripology ruler--very accurate.

My first thought was the surface the mat is on, must be firm like you did using solid wood.

I had a ruler I loved and always used but noticed that the corner was slightly chipped off with so much wear and tear on it. I just had to go buy another one and it made a big difference in getting straight cuts. I also find that if I cut shorter strips it helps keep them straight

I have had this problem also and then started using the other side of the ruler(until I get a new one) Also I found that if I folded the fabric more that twice, I would get that "bow". When you buy fabric, it does not come of the bolt in true grain, that could also cause the problem. To get the true grain, cut on the original fold, about 1/2 inch and rip. Then trim the raw edge. Bearisgray has some great advice. I am going to buy a new ruler.

I have replaced rulers because they wear out but never thought of checking for a bowing issue. I get rid of them when they have nicks in them or the lines wear off but never thought that some issues would be caused by bowing. Now I go and check all my rullers. Including my new ones.

I just did the ruler test and discovered that I could easily get a layer of fabric under a couple of spots. I moved the ruler to another spot on the cutting table with the same result. I then moved it to my sewing table and I was not able to slide the fabric under it. So I have concluded that my ruler is fine but my cutting table isn't. Do you think that will be an issue when I use my cutting on the table?

i mentioned this a few posts up. It definitely affected cutting accurately for me. Plus I kept changing blades because I thought that was the problem. Now I use a better cutting surface and things are more accurate and blades last
longer.

As often happens - there may be several different causes of a problem - or several causes all contributing to the same problem.

I have also had issues with cutting on one of those folding tables where there is some "give".