I am having the same issue, everything else is completed but Sunreaver Onslaught will not pop!
He’s proof, and I’ve been doing Sunreaver Onslaught quests daily after I reached exulted, and nothing.
https://i.imgur.com/4IQaYSM.png
I too have reached exalted with the Sunreaver Onslaught. It shows exalted in my reputation list but I do not have credit in MOP Remix for being exalted. It is the only achievement in MOP remix that I need to have it completed and I would like to be able to complete it before REMIX ends.
My reply was just a list of links to look up the achievement and a sorry Gms can not give achievements out.
update: achievement is fixed… now have all 148 special remix achievements! 
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Can confirm, also got my missing achievement. 147/147 for Remix plus the feat of strength.
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