Using a Layer Mask breaks my Brush Tool

When I add a layer mask onto my PNG image. I get this extremely undesired diamond pattern whenever I use my brush tool on the layer mask. Why on earth is this happening and how do I fix it/ keep it from happening in the first place?

To Recreate the problem:

1. Use Color Range 

2. Convert Color Range Selection into a Layer Mask

3. Equip the Brush tool and use it with the Layer Mask selected.

Follow these steps, you will inevitably get the extremely weird diamond pattern to occur.