@mkelsey thanks for your reply.
This works for a simple volume. However, if my geometry is defined with a G4AssemblyVolume and I replace detectorLV within ConstructSDandField() with a logical volume associated with one of the G4AssemblyVolume components, it fails. When I do this, ProcessHits() in my SensitiveDetector class is never called, which is obviously an issue. This is why I posted this post.
Do you know why this is and how I can solve it when using G4AssemblyVolume?
I could, of course, just do away with G4AssemblyVolume and define each instance of the same geometry individually. However, this is rather tiresome when G4AssemblyVolume does such a good job from a detector construction point of view.