First of all, lag is a huge problem especially if the map is very large and consisting of many meshes/particles. A simple solution of massive lag reduce is by going to your "Options>Video>Water Reflection and unchecking the box. While you're in the videos tab, make sure to turn your "View Distance" all the way down and restart your game.
If the problem persists, I do suggest redownloading the map once making sure all of its files have been deleted (if they aren't all deleted when redownloading, you must check Replace" when it asks you to)
Lag is the #1 reason for bad tokens and crashes so make sure it's out of the way as much as possible (particles cause much more lag than meshes do)