I've been having issues with select and mask ever since it as changed from the old refine edge. The refine age tool makes the strangest of selections when I'm using it. I tried following numerous tutorials and don't think it was user error. Plus I could never use the onion layer view as it got a program error message everytime. I was hoping this recent update of Photoshop CC would correct it, but it's made it worse. Now I can't even open "Select and Mask". When ever I try I get a message saying `"Could not apply the workspace because of a program error.
from my experience, its a GPU issue. go to preferences->performance and disable using graphics processor and see if that resolves it. if it does you might want to update you GPU. it could be a bug related to certain GPU's.