  Using effective-range expansion for the two-body amplitudes may generate
spurious sub-threshold poles outside of the convergence range of the expansion.
In the infinite volume, the emergence of such poles leads to the
inconsistencies in the three-body equations, e.g., to the breakdown of
unitarity. We investigate the effect of the spurious poles on the three-body
quantization condition in a finite volume and show that it leads to a peculiar
dependence of the energy levels on the box size $L$. Furthermore, within a
simple model, it is demonstrated that the procedure for the removal of these
poles, which was recently proposed in Ref.[1] in the infinite volume, can be
adapted to the finite-volume calculations. The structure of the exact energy
levels is reproduced with an accuracy that systematically improves order by
order in the EFT expansion.
