sorry if this is a common issue; I’m new to modeling and I couldn’t find any answers out there.
I used Duplicate Special in Maya for symmetry, mirroring the objects as instances for real-time updating.
Everything seemed fine in ZBrush…

… but the front faces of the instances were invisible as shown below:

Is it some kind of backface culling issue?
My apologies if this should be in the Maya subforum.