Can't export terrain into any usable format

I'm having trouble exporting a terrain to FBX. The terrain came from an Ancient Desert Town environment pack I bought in the Asset Store and runs great in Unity. However, when I try exporting it into an FBX, it crashes. I've tried three different FBX export plugins, and each of them have a different error. Clearly, the problem is with the terrain itself, but I can't figure out what.

When I use the Unity FBX exporter, it creates an FBX but the file is only 10kb, and when I try importing it into Maya, it just says "Unrecognized File Type".

I tried using Export2Maya as well but it freezes during the export and just says OutOfMemory Exception: Out of Memory. It freezes at "Writing DesertShape UV Data"

I also tried using Sator Imaging's Unity Terrain FBX plugin which claims to be specifically for terrains but it also froze while "Exporting Vertices" and ran out of memory.

It seems like there's an issue with the terrain itself, but how do I fix this? I tried exporting it without textures as well (just the raw heightmapped mesh) and it still froze. Switching static on and off also had no difference.

Any help would be much appreciated!