Photo disappears when zooming in

In Develop module when I try and zoom in to edit a small section of the image the photo enlarges a litle bit then goes black and I have to zoom out to see the image again. This happens regardles of what is selected in terms of  enlarging from image size Fit, Fill, or 66% etc etc 

Using MB2 with latest Apple and LR version downloaded ...please advise how to fix this?

Thanks 

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