Your Landscape Material set up looks a bit incorrect. You seem to be using the Layer Blend approach, but are not using the alpha with any of your texture samples. Have a look over the Documentation for Landscape Materials and double check your approach. There are a few different ways to go about getting your material to paint correctly.
Here is how I have my Landscape Material set up for your own reference.
Notice how I am using all of the inputs for my ‘Layer Blend’ nodes and none of my ‘Texture Samples’ are sharing ‘Landscape Coords’ both of these are important.
If you are still having problems try creating an new AnswerHub post so we can give you more individual support.