That's odd. If it starts happening after a little while, it's usually a sign that your graphics card is starting to age. But if it doesn't occur on other games, that's probably not the case. Deleting your cache might work, though I think it's unlikely, since your problems don't occur right away. For me, my game cache is located under C:\Windows\.jagex_cache_32\runescape. You can safely delete the entire folder, as far as I know. You could try to change your display mode from OpenGL to Direct3D, or vice versa, in-game. You can access those via the "custom" button in the graphics options menu. If that doesn't fix anything, you could try tuning down various graphics options. While your PC may have handled RS just fine in the past, the game engine has steadily been changing, and something might've changed that causes issues. Swiftkit, hrm, I don't know. Probably not, but I have no idea how Swiftkit determines what Java to use.