I was having this issue too, oddly it was Google Chrome causing it =S. I was also getting FPS drops down to 0.5fps with more than 2-3 people/monsters on the screen. This was very out of the norm. Around that time videos from non-youtube sites wern’t loading. After I went into Chrome extentions, I disabled flash player (pepflashplayer.dll).
(chrome://settings/content)
(Plug-Ins->manage individual plug-ins)
(disable the one shown in picture)
.
After disabling this thing, my videos were loading on all sites, and my FPS on Tree of Savior returned to what it normally is.
.
You can just as easily re-enable it if it’s not helping anything disabling it.