  The correct description of the standard Casimir effect for periodic boundary
conditions via light front formalism implies in these conditions imposed at
fixed Minkowski times [Almeida {\it et al.} Phys. Rev. {\bf D 87}, 065028
(2013); Chabysheva and Hiller, Phys. Rev. {\bf D 88}, 085006 (2013)] instead of
fixed light front times. The unphysical nature of this latter condition is
manifested in the vacuum part by no regularization yielding a finite Casimir
energy density [Lenz and Steinbacher, Phys. Rev. {\bf D 67}, 045010 (2003)]. In
the present paper, we extend this discussion and analyze the problem of the
light front quantization with simultaneous presence of a thermal bath and
boundary conditions. Considering both the oblique light front as well as Dirac
light front coordinates, we show that the imposition of periodic boundary
conditions at fixed Minkowski times recovers the expected behaviors for the
energy density and Casimir entropy. We also investigate how the unphysical
nature of the periodic boundary conditions imposed at fixed light front times
manifests in the thermal part of the energy and entropy, showing that in the
classical limit the Casimir entropy decreases linearly with the temperature
(not becoming independent of the temperature as expected), and also that the
Kirchhoff theorem is not respected.
