It looks like you guys are trying to use an imported texture in the content browser and then hook that up to the height input inside the material? if so that is not how it is meant to be done.
You need to import your splat maps using the landscape layer paint tool by right clicking the layer and choose “import from”. And as far as I know, there is no way to use the channel packed splat maps, you will need to render a unique grayscale layer for each layer.
The way you use the “Layer Blend” node is not necessarily wrong since you can do whatever you want with it, but it is definitely not how it was designed. The “Height” inputs there are meant to be heightmap textures that match your layers. This gives the blending some broken up heightblend modulation which increases the visual quality. It looks like you are trying to hook up an actual alpha as a height which means you are essentially modulating the stored painted weightmaps with another painted heightmap which doesn’t really make any sense.
You certainly can use your own imported RGB splatmap, but don’t expect it to have any interaction with any other landscape features like painting or procedural foliage, it will simply exist as a texture in isolation. The only tool that can leverage it is the landscape grass since you can bake anything to the grass output.
Hopefully that helps.