This looks like the “lighting preview” debug decal being projected on the material in editor. Build your lighting and it should go away.
Hey,
i created a landscape a few months ago and i can remember using a “preview” material on accident and i thought i had removed it. Still, i can see the preview-text on top of any other material or mesh.
Hope you can help me fix this, I´m really frustrated because I don´t know how.
Thanks!
Thank you SO much! You are right, it is the Light Source, thanks 
Thank yout, it worked! I was so frustrated haha, thanks man!
Another way, if using baked lighting (static / stationary), is go to Project Settings > Rendering > Optimizations and disable “Render Unbuilt Preview Shadows in game”. The text can also be changed, and that’s somewhere in Project Settings or Preferences too.