Non-repeat wrap mode used on a texture with non power-of-two dimensions, may cause it to be rendered incorrectly.
Luna targets WebGL 1 API, which is roughly equivalent to OpenGL ES 2.0. This family of graphics API doesn't support the sampling textures with addressing modes other than
Repeat, if the texture's dimensions are not power-of-two.
Medium / High
There are two options of how this warning can be eliminated:
Use Unity's "Non Power of 2" option to automatically resize the texture to become a PoT texture (Luna does respect this setting as well). This option can be found in texture's import settings:
Resize the original file in any graphics editor (Photoshop, Sketch etc) to make sure both width and height are power of two (2, 4, 8, 16 ...)