In the bilayer quantum Hall (QH) system at the filling factor ν = 1 , the parallel magnetic field B ∥ penetrates between the two layers as sine-Gordon solitons, creating a soliton lattice for B ∥ > B ∥ * with B ∥ * a certain transition point. This regime is called the incommensurate (IC) phase. The diagonal resistance R xx has been observed experimentally to exhibit an anomalous peak just inside the IC phase though the Hall resistivity R xy shows a well-developed plateau. We interpret this phenomenon as an evidence of the soliton lattice formation: A nontrivial transmission coefficient arises when an electron collides with thermally fluctuating solitons, as leads to an anomalous increase of the diagonal resistance R xx in the QH regime at finite temperature.