Hi! I was decorating cookies and used a new brand (my usual brand was out of stock at the time) of disposable piping bags. I used to be able to use my old brand of disposable piping bags tipless (no coupler or metal tips, just snipped the ends of the bag), and the icing would pipe out rounded strings of icing. 

These new bags though -----NO DICE!

The icing that comes out from the new bags are flat looking. Like a ribbon, and not rounded.

I noticed these bags have a more prominent seam. My old piping bags had pretty non-existent seams, the seams  just looked like a long crease down the side of the bag. 

Could the seam on the new bag be the culprit? Anyone have experience with this? 

yes it is the seam -- you could try trimming off some of the seam allowance and creasing the tip of the bag in the opposite direction to round it out --kwim

best to you