I have 535 Neltharax and when running script to check watermark I have ilvl 0 on mainhand. Also did not received achievements for upgrading crests even when I have full 502+ gear in every slot.
I did not received any other weapon this season yet.
Probably weapon shenanigans. I’m not 100% sure how it works but I think 1H and 2H weapons are counted differently for discounts and those achievement.
Edit: I see you’re talking about your hunter so I guess they don’t use 1H weapons. Could be a bug I don’t know for sure.