  How superconductivity interacts with charge or nematic order is one of the
great unresolved issues at the center of research in quantum materials.
Ba$_{1-x}$Sr$_{x}$Ni$_{2}$As$_{2}$ (BSNA) is a charge ordered pnictide
superconductor recently shown to exhibit a six-fold enhancement of
superconductivity due to nematic fluctuations near a quantum phase transition
(at $x_c=0.7$). The superconductivity is, however, anomalous, with the
resistive transition for $0.4 < x< x_c$ occurring at a higher temperature than
the specific heat anomaly. Using x-ray scattering, we discovered a new charge
density wave (CDW) in BSNA in this composition range. The CDW is commensurate
with a period of two lattice parameters, and is distinct from the two CDWs
previously reported in this material. We argue that the anomalous transport
behavior arises from heterogeneous superconductivity nucleating at antiphase
domain walls in this CDW. We also present new data on the incommensurate CDW,
previously identified as being unidirectional, showing that is a rotationally
symmetric, "4$Q$" state with $C_4$ symmetry. Our study establishes BSNA as a
rare material containing three distinct CDWs, and an exciting testbed for
studying coupling between CDW, nematic, and SC orders.
