So it’s been months since this was first discovered and discussed, and even admitted by Blizzard to not have some kind of work around or fix at that time. Now here we are eleven months later from that post, and we still have no fix for this.
For people who might not know, glyph of voidling essentially cannot be removed from the priest. This also appears to happen with sha and lightspawn. Even with vanishing powder being used, upon relogging, the priest will have the glyphed version once more and it will even show the glyph is no longer applied.
With TWW, shadowfiend received a cosmetic glow up and now has an infinitely more appealing appearance than any of the glyphed versions in my opinion. The fact I cannot use the much better aesthetic version of this spell because of a bug which has not been addressed in about a year feels bad.