I'm trying to create a simple shape with a gradient, and I made it by first making a circle, splitting it in half with the scissor tool, and then manually offsetting the bottom half to the left to create a single thick sine wave. I then joined the two paths.
At this point I applied a gradient stroke, and that's when the rectangular artifact shows up within the gradient.
I expanded the appearance to see what was going on, and that's what the 2nd image is.
Please can anyone help me create just a smooth gradient along this path?
Which version of Illustrator are you using?
Also, can you share this sample Illustrator file (.ai)?
In the center of the wave there should be just 1 anchor point.
Can you check that?
If you didn't move the half path precisely before joining them then there would be 2.