I needed more detail in this barrel that I made from flat plane and using curve modifier to bend it, but when I add more cutts they are ignored when bending and the shape stays the same as if they were not there. Also when I fast created new model it works just as expected and I have no idea why on my original model they are not working. There is also a problem with both of them creating these vertical distortions when shade smoothing.
Here is what I found-all that that unnecessary loopcuts were causing the issue. It is probably because you used mirror modifiers to make the barrel. Mirror modifier just make a duplicate of the mesh and mirrors it. It does not merge the vertices to the original mesh.
In your case the easiest way to solve it is by selecting all those edges (which you have beveled) except any one among them by alt+shift + RMB and then delete them by pressing X.Dont forget to switch off all the modidifiers except curve modifier before selecting (Select the edge and press Gtwice tp slide the edge) Which will get u this: To solve it in the proper way, you can apply the mirror modifier and box select the vertices and merge them with altM > merge at center .(You wont even see the vertices cuz they are too close to each other).OR simply use the merge option in mirror modifier.