  We address the origin of the magnetic-field independent -|A| T^{1/2} term
observed in the low-temperature resistivity of several As-based metallic
systems of the PbFCl structure type. For the layered compound
ZrAs_{1.58}Se_{0.39}, we show that vacancies in the square nets of As give rise
to the low-temperature transport anomaly over a wide temperature regime of
almost two decades in temperature. This low-temperature behavior is in line
with the non-magnetic version of the two-channel Kondo effect, whose origin we
ascribe to a dynamic Jahn-Teller effect operating at the vacancy-carrying As
layer with a C_4 symmetry. The pair-breaking nature of the dynamical defects in
the square nets of As explains the low superconducting transition temperature
T_{\rm{c}}\approx 0.14 K of ZrAs_{1.58}Se_{0.39}, as compared to the
free-of-vacancies homologue ZrP_{1.54}S_{0.46} (T_{\rm{c}}\approx 3.7 K). Our
findings should be relevant to a wide class of metals with disordered pnictogen
layers.
