Landscape in-game is different from landscape in editor. How to fix?

I’ve been using the landscape tools to adjust my landscape to fit newly-added buildings. I recently added a small ramp using the ramp tool, to smooth a drop-off in the ocean. Since doing this, every time I build my development game, the entire landscape has been somehow “smoothed” - corners of rock have vanished, an entire outcrop is gone, flat planes with buildings on are now ramps.

None of this shows in the editor, it’s only in the build. How do I make the built landscape match the editor landscape?

edit
To add more information to this… It’s now happening in the editor as well. If I access the landscape tools and make changes, the changes I made before come back. When I save, it reverts to the smoothed version. I tried turning off texture streaming for the textures used in the landscape material, but to no avail. And the build is still showing the malformed terrain, with broken collision boxes.

I have a backup from before this started to happen, but I really don’t want to lose the amount of work I’ve got done in that time. Any help and suggestions would be welcomed.