I don't think I see this on mine, but I don't see this on your photo either, mine look similar to your photo. If you had the old Ananda, I think it previously (pre-2020 or so?) didn't have the black fabric mesh, this was an update. My Ananda has it.Yeah it's a defect i think. I can also see the traces on the diaphragm have unevenness on my unit. If you shine light on it, you can see bumps, wrinkles and cuts on the traces i don't know if it's related. I never noticed this with my Ananda.
Hard to capture on photo.
With regard to your sub-bass distortion test- playing a 20Hz test tone at very high levels, sitting on a desk, that goes away when you put them on your head- I'm not sure this is really a realistic test, they are not designed to be used to play very low sub-bass test tones on a desk, they are designed as headphones to be used on your head. I actually do notice with this, if I put them on, I get a variation in response as I move my head around, it seems if I move my head so one side cup now has a wall 60cm/2ft away from it, that actually has a noticeable effect (on very loud sub-bass tones, specifically). I'd put this down to their being open backs, stuff outside the headphone actually does impact on the sound. So I wonder if this is related, that when you have them on the desk, they are just too close to a solid surface, and that is interfering. I don't notice it with music at normal listening levels.
Do you have any perceived issues with them actually playing music?