Import Real World Locations Into UE4

Please help me why my map gets split in half.

I’ve followed this video

and I got this result →


Why my map is split and the other half is lower ? Please help how to make it even and joined together.

Did you import all the terrain files at the same time, i would unload all the terrain files then re-import them, and make sure when you import them you import them all the same time, ie, highlight them all then hit the open button.