I have a loft that for certain dimensions the loft stops showing the surface. I can't post my model due to privacy concerns and I have contact my VAR. 

If manipulate one variable it will work for periodic ranges however certain ranges the loft either stops working or the surfaces stop showing with no loft error. I have merge tangent faces and merge results select. I also have show preview and it appears to show the correct profile in the preview, it just doesn't actually populate.

If I un-select merge tangent faces, the loft will work with no issues. 

Has anyone else ran into this issue before?