3D Paint and Channels

Why are you painting in the 3d layers channels?  Do you want to change what the sphere surface look like.  If that is what you want  to do you should paint on the 3d Object surface material properties.  Paint on 3d things like its opacity map,  Bump map, surface etc,   You are not dealing with 2D pixel layers. There a lot of geometry involved with 3d layers.   Do you normally paint on 2d layers channels other then Layer mask channels?  What are you trying to do painting on these channels. The are just gray scale maps and your screen capture shows you had no problem painting on the blue channel as shown by its gray scale thumbnail.. You lowered some red son green and some blue areas changing white to gray and black.  Some of the area effect the sphere.   If you paint one the Sphere surface work psb document and also have the document with the 3D layer visible in Photosh window. Photoshop will display a cross hair on the 3d object  so you can know where on the 3d surface you are painting on in the surfaces's flat view in the PSB work document.  When you close and save the psb the 3d object surface will be updated in your document with the 3d object.  You paint on the flat layer not the channels in the PSB document.  Why are you trying to paint ib its channels? How did you open the PSB file you show.  If you opened the surface texture the whole canvas should have been red Like I showed not white like yours Switch between document to rotate the 3d object so you can paint on hidden area by rotating them into view....