Secondary Jagged Stroke
Mac OS Monterey 12.0.1
I have been drawing lines with the line tool and expanding and bending them using the Anchor Point Tool. Sometimes Illustrator creates a secondary line alongside my smooth one that is jagged. It is still visible if I zoom in or out but I don't think it's really there (as a vector path). It is visible in the middle of my screenshot.
Aaron Firouz commented
I've been experiencing this same behavior on my new 2021 MBP 14" (M1 Pro) with the latest OS (Monterrey 12.1). A lot of my artwork has "junk" along curved lines. As Egor mentioned, this only happens when GPU acceleration is enabled; disabling it seems to 'fix' the problem. See the attached screenshots.
I didn't notice this on my Intel MBP, but I didn't use it much and mostly used Windows PCs before this; I never noticed this problem on Windows.
Philip, it's one of many existing GPU rendering bugs Ai has.
Can you make a copy of your file, remove everything that does not influence the bug, and share it here?