You probably placed the landmarks in the wrong place. Remember that the player starts in the next level at the same distance from the landmark as he was in the previous level - the landmark entities are a solid point, considered to be the same location in both levels (while they don't have to be placed in the same spot, they're the comparing point, so to say).
In other words, if you're 20 units below the landmark in level 1, and the trigger_levelchange is triggered, you'll end up 20 units below the landmark in level 2.