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

[ispano]

Two weeks after this supposed change, and they still disappear everytime they spawn when enough people are attacking them (read: always).

Display priority is just a client side change. The real issue is too many people in one spot for the server to handle, so it's likely it literally just cannot handle it all and things don't work right. Which tells you that too many people are doing the content, and that's because the rewards are too high. As they always say "this is why we can't have nice things"