Attachment uploader is bugged so here's an imgur link. If that doesn't show: On the HUD hero portrait, in place of the transparent neck portions of the cosmetic, there's a mostly opaque dark red color. There's a small portion of polygons that fades in and out of transparency as the character moves during her idle animation, so maybe it's related to angle?
(this screenshot was taken with other cosmetics, but the bug also occurs if the rest of the loadout is cosmetics-free)

This bug is inconsistent: sometimes there's no issue and sometimes the transparency is fine but instead the shadow cast by the hair cosmetic (Magnificent Flame) onto the character's head will be bugged/cut off.
This bug can be triggered by reloading the hero. In demo mode for example, switch to a different hero and then back to Lina for a (pretty high) chance to trigger this bug.
This bug only seems to occur on the HUD hero portrait. It doesn't occur in the pregame hero selection menus or the ingame world model of the hero.