Landscape materials going insane

So I added a bunch of tree meshes to a scene I’m making, having previously made the rest of the landscape.

It’s hard to illustrate with a still image, but suddenly my terrains material and textures are going crazy! Flickering between the different layers in patches very rapidly, especially as I move the camera closer! There were no issues prior to adding these static meshes, how did they cause it? Additionally this flickering seems to be undoing any additional terrain painting I do.

Okay, scratch that. Somehow I duplicated the landscape and that was causing it. Quite unsure how that even happened.

you might have held down the ALT key while moving/rotating it which will create a duplicate.