Hey PinkPanteRus,
I have seen this issue before with multiple textures that utilize a layer blend. Essentially you are running out of samples for your textures. You are limited to four samples per material with standard settings.
Here are steps to create a wrapped Sample Texture Material
1.) Inside of your Texture Samples go to the Details Panel
2.) Under Material Expression Texture Sample > Sampler Source > Choose from the drop down choose Shared Wrap
3.) Do this for all of your Texture Samples
If you are using a landscape for this.
1.) Apply your material to your landscape
2.) In your Landscape > Pant panels where you have your target layers listed.
3.) Go to one of your target layers and click the little plus symbol on the far right.
4.) This will add a _LayerInfo node.
5.) Under the drop down next to the target layer you just created add that Layer Info to that Target Layer
This should clear this up.
Thanks,