A simple art brush made of several parallel rectangles has unexpected results when the Zig Zag effect is applied with smooth curves instead of sharp angles. Changing the number of stripes and/or the number of zigs alters the errors. Some of them are kind of pretty but I think I'd rather just see this working as expected.

I reproduced this on an M2 Mac running Illustrator 27.8.1, in both CPU and GPU rendering modes. I'm not sure what the person who originally observed this and got me investigating was using.

Uservoice isn't letting me upload an AI or a zip, demonstration file is here: http://egypt.urnash.com/media/blogs.dir/1/files/2023/12/zig-zag-art-brush-glitch.ai_.zip