In the attached file you can see two identical gradients applied to two identical paths. One looks fragmented and shattered, something is really off with the tessellation. The other one is fine.

If you select the weird one disable the Overprint Stroke option in Attributes — it works fine. Choose another and enable the option — it gets corrupted as well.

If you copy either in a new file — the behavior continues. But if you try to reproduce this bug anew in a new file from the scratch — it won’t get reproduced.