Region Union Omits Certain Curves

Dear Forum,

My situation:  I take any Breps, cut sections through them like floor plates, join the curves in case they're broken, make sure they are closed, group the coplanar (same floors) curves into lists, then apply Region Union in order to define the floors plates as single polylines.

For some reason it seems to omit certain floors, even though, as a test, if I were to bake those curves, reference them together, and apply the Region Union component, they work.

Thank you for your time,

Ognek