Terrain flattens when I switch to Landscape Mode

Hi, I am having an issue with my terrain and the landscape tool. When i open the level and hit play everything is normal, but as soon as I switch to Landscape editing, one of my terrains flattens completely…the paint stays the same…
It happened a few times, at first I thought it was because I used landscape layers to add a spline mesh…but the second time it happened after I added a new Level with a terrain
I am using World Composition