The ID for this issue: UE-29433
I have figured out what is causing this bug to occur and how to prevent it from occurring in your projects. It’s actually a really simple problem.
Why this issue is happening: Landscape’s have their transform location set to their positive X and positive Y corner. When you create a new landscape with the “Landscape” Modes tab it will offset the transform location in order to center the landscape in the world. When you create an adjacent landscape level World Composition places the new landscape level directly next to the previous level’s bounding box in the direction you chose. However, the new landscape proxy inside the new level then inherits the offset transform location from the original landscape thus positioning it in the wrong location.
How to prevent this from happening to you: It’s as simple as opening the level with the original landscape in it and resetting the original landscape’s transform location to X = 0 and Y = 0. You must load the level by itself and not through the persistent level or else the landscape’s transform will be grayed out and non-editable. Any preexisting levels with a landscape proxy for the original landscape will all have their transforms updated once those levels are loaded afterwards. Now, whenever you use the “Add Adjacent Landscape Level” option the new landscape level will always be placed correctly.
How I suggest this issue be fixed: When World Composition positions the new landscape level it needs to take into consideration the transform location of the landscape in addition to the level’s bounding box. As simple as that.
P.S. I know this post isn’t a question, but the issue’s page said to post here on the AnswerHub if I have comments or more details.