Since 11.1, my death knight’s back-sheathed transmog of mythic The Devouring Cold has been acting a bit funky. Whenever I log in, a copy of each weapon in both sheathe positions is displayed (client-side only, as no one else can see it). The only way to fix the issue is to clear the transmogs and re-apply them, as unequipping the weapons only removes the back-sheathed versions, with the hip-sheathed versions stuck until re-applying the back-sheathed mog. See the below screenshot.
https://imgur.com/a/Ix9z4Qy
To further make this peculiar, my warband camp screen only shows the hip-sheathed appearances for that character, even though the back-sheathed is the chosen appearance.