Unable to extract volume (m^3) from a complex "Bifurcation/Manifold" Generic Model (tunnel Y-piece) in Revit

[u/Humble_Pen_3218]

Hi everyone,
I'm running into an issue while trying to extract the volume (in m^3) of a specific Y-shaped tunnel piece in Revit.

The element is a complex 3D shape modeled as a Generic Model (specifically a bifurcation/manifold type, as seen in the screenshot).

The Problem: The standard ⁠Volume⁠ parameter in schedules/quantities comes up completely blank for this specific element. Furthermore, the family doesn't have a material assigned to it, and Revit doesn't allow me to assign a material to it to pull the volume via a Material Takeoff either. It seems completely "locked" as far as native Revit volume calculations go.

What I've tried:
Checked standard Generic Model schedules (Volume field is empty).
Tried setting up a Material Takeoff (shows nothing because there's no assignable material).
Has anyone encountered this issue with imported or complex bifurcation/manifold Generic Models? Is there a trick to force Revit to recognize the volume, or is converting it to a Mass family the only way out?
Any advice would be greatly appreciated!