Surface disappears when join

Rhino Rhino for Windows
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Hello, there. So I do not have much experience, I am only using the trial version for my classes. I created some sort of object from many, many surfaces and when I try to join all of them, the front surface simply disappears. I also tried to use the boolean union as I am trying to make a single object when clicking on it, but of course, boolean union failed. What can I do to make it a single object?

I have also tried to explode the surfaces and to join them again, but the front surface disappears again. Any advice please?2

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1.jpg1364×728 221 KB

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without the file it’s hard to find the correct answer but I guess that the problem can be two o more ellipses touching each other, causing manifold edges over the front surface.
when this happen, the surface can not generate the mesh representation correctly.