How not to mess up landscape material in paint mode when I change something?

Hi, I am a bit tired of finding out my landscape material is mess up after I did a change (value/par updated, texture replaced, …) and I want to know :

  1. Why I have these problems (blue hand drawn circle)?
  • big question mark (only resort is to delete it???)
  • material image not showing up anymore
  1. How to avoid messing up my landscape material in the paint mode when I change something in the material itself?

Does anyone know the answer to this problem?