client delay during hunt/fate

hi guys, i have suddenly stumbled upon a game breaking issue. my ff client seems to have delay during any fight involving large number of players such as hunt or fate. for example when i press any skill it will show the damage in the next 30 seconds or so. chat log is not delayed though, i can chat real time just fine in LS or party. my ping also stable.
my pc has i7 4790k, RX 480, and 16GB ram, and during the hunt i dont see any jump cpu/gpu load and the fps still remains.
have any of you guys encountered this and know how to deal with this problem?