Yes, that's how the blend tool works. It creates multiple copies (a loooooooot of copies). The secret is to make so many copies so close together that it doesn't show. The copies are still there and will completely ruin your relationship to the printing company. This method will only work when you convert the artwork to pixels for output.
So maybe you don't have enough copies. But maybe the GPU acceleration messes this up. Try View > Preview on CPU.
If you want to print, try either the plugin opo or the plugin Stylism or this method: