Lofted cut but retain every part

Hello, everyone.

In these pictures, I intended to split the tube into two parts by using particular lofted cut geometry. However, it turned out that the small part of the cut tube (the one inside yellow prism) also disappear, while I actually want to keep all parts as they are placed. How can I keep all parts while can still perform splitting on the tube? What feature should I use actually? Thank you for your kind attention.

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