  Quantum transport simulations are rapidly evolving and now encompass
well-controlled tensor network techniques for many-body limits. One powerful
approach combines matrix product states with extended reservoirs. In this
method, continuous reservoirs are represented by explicit, discretized
counterparts and a chemical potential or temperature drop is maintained by
external relaxation. Currents are strongly influenced by relaxation when it is
very weak or strong, resulting in a simulation analog of Kramers' turnover for
solution-phase chemical reactions. At intermediate relaxation, the intrinsic
conductance, that given by the Landauer or Meir-Wingreen expressions, moderates
the current. We demonstrate that strong impurity scattering (i.e., a small
steady-state current) reveals anomalous transport regimes within this
methodology at weak-to-moderate and moderate-to-strong relaxation. The former
is due to virtual transitions and the latter to unphysical broadening of the
populated density of states. Thus, the turnover analog has $five$ standard
transport regimes, further constraining the parameters that lead to recovery of
the intrinsic conductance. In the worst case, the common strategy of choosing a
relaxation strength proportional to the reservoir level spacing can prevent
convergence to the continuum limit. This advocates a simulation strategy where
one utilizes the current versus relaxation turnover profiles to identify
simulation parameters that most efficiently reproduce the intrinsic physical
behavior.
