I believe you r having a multi-mesh model. From my experience, for a multi-mesh model, in SMV, there r two options, one is "Multi-slice" and the other is "Slice". Choosing multi-slice will lead to disappearing region of slice like what happen in your screenshot and I have experienced that too. What I have done it simply choose all slice at that elevation under "slice". Sounds stupid but works for me. Hope it can help!