July 15th Hotfix Notes - "S rank elite marks will have top display priority."

[Nekodar]

Square Enix logic: Egis and fairies, other players, NPCs, a tree and even a few bushes are more important on the rendering priority list than a mob trying to kill you. (In that order, too.)

Except it's not client side rendering that is the problem any more.
Client side works fine when the number of people is reasonable, and the display priority made sure that the elite mark was visible within those parameters, as it could disappear for some people then too.
The problem is server side as was explained already.
Applying the same fix as they did to Odin/Behemoth takes time, and even then it's only reasonable to expect that to be done for the S-ranks.