I purchased the Yaungol Slayer’s Belt Cosmetic from the vendor on the Timeless Isle, however it did not count towards the belt on the Yaungol Slayer Battlegear Heroic set which has the item needing to be Epic quality. The only other version of this item according to Wowhead was from MoP Remix which is no longer live. Also the Heroic pieces of Ranger’s Chain of Unending Summer and Shadowgrip Girdle have the same look as their LFR version and do not match the rest the alternate pieces for the Heroic set.
Also since I have the appearance unlocked there is no longer a hint in the Collections tab, though it likely would just say World Drop. Using mods All The Things and Wowthing there is no location or drop for this piece. Is there any confirmation that this item is even available currently? I have submitted a bug report in game as well.
probably not going to have any priority but just having this 1 item missing from the set even though I have the appearance is really annoying.