  Photonic platforms invariant under parity ($\mathcal{P}$), time-reversal
($\mathcal{T}$), and duality ($\mathcal{D}$) can support topological phases
analogous to those found in time-reversal invariant ${\mathbb{Z}_2}$ electronic
systems with conserved spin. Here, we demonstrate the resilience of the
underlying spin Chern phases against non-Hermitian effects, notably material
dissipation. We identify that non-Hermitian,
$\mathcal{P}\mathcal{D}$-symmetric, and reciprocal photonic insulators fall
into two topologically distinct classes. Our analysis focuses on the topology
of a $\mathcal{P}\mathcal{D}$-symmetric and reciprocal parallel-plate waveguide
(PPW). We discover a critical loss level in the plates that marks a topological
phase transition. The Hamiltonian of the
$\mathcal{P}\mathcal{T}\mathcal{D}$-symmetric system is found to consist of an
infinite direct sum of Kane-Mele type Hamiltonians with a common band gap. This
structure leads to the topological charge of the waveguide being an ill-defined
sum of integers due to the particle-hole symmetry. Each component of this
series corresponds to a spin-polarized edge state. Our findings present a
unique instance of a topological photonic system that can host an infinite
number of edge states in its band gap.
