I'm a European player, but still playing on Sargatanas as I was migrated there from 1.0 and have all my friends / LS stuff there, but since a few months I do experience the same issues.
Especially in dungeons/raids the stuttering is very clear. Mobs/characters not moving for 0.5-1s every few seconds, my Red mage acting up (instead of the slow/fast/slow/fast spells it often goes slow/slow/slow) or using swift cast -> raise still starts to cast slowly after using the swift cast.

I never really had these kind of issues until like 2-3 months ago?

I've tried using my alt character on a EU server, but I see the same issues there.