Moving this over to the Game Help board since you are seeking assistance. The Game Discussion board is for posting game-related discussions, rather than a place to seek help.
If you have recently installed any add-ons such as markings, items, or any modifications, it's possible that you have installed them incorrectly or the lag is taking a toll on your computer. Be sure you have installed everything correctly and even go for a re-install if you aren't sure. You can try removing any add-ons and see if the issue still occurs, as well. c:
