I create new project - add a terrain - add some textures - with diffuse and normals - add a material and set it to terrain specular.
Play - all good - stop - hangs Unity
After some playing around i was able to narrow it to - Unselect static on the terrain - you can play and pause as you like. Select static - BAM same behaviour.
Further experimentation without custom material and same thing - you make it Static and when you stop play it hangs editor.
When you mark the terrain as static, it starts baking global illumination / lightmap on it. It’s currently more or less broke with terrain’s, especially large ones.
If you actually want lightmapping on your terrain, then go to the new “Lighting” tab and change your realtime resolution to something tiny like 0.1 and change your baked resolution to something like “2”. You might also want to uncheck “continuous” so you can bake manually. Then you might be able to bake your lightmaps, or you might get stuck at that stage until a later beta. (All of my terrains currently work but for some others they don’t - see elsewhere on this forum - lots of people can’t bake with Terrains in their scenes apparently).
If you don’t want lightmapping, then simply unselect “lightmap static” in the static dropdown in the inspector for your terrain.