Regarding the degradation of o-chloro-1-chlorobenzene during distillation

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We produce o-chloro-1-chlorobenzene. During the distillation of the crude product obtained after chlorinating o-chlorotoluene (with approximately 58% o-chlorotoluene and around 40% o-chloro-1-chlorobenzene in the crude product), we encountered a puzzling issue: after some of the o-chlorotoluene was removed from the top of the tower, the concentration of o-chloro-1-chlorobenzene in the reactor decreased compared to its level in the initial crude product, while the concentration of o-chlorotoluene increased. It seems as though o-chloro-1-chlorobenzene decomposes upon heating and converts back into o-chlorotoluene, which is really hard to understand… Additionally, chromatographic analysis showed no other unknown impurity peaks in the material inside the reactor after it deteriorated. Please advise those who are familiar with this product – could it be due to damage to the enamel-lined reactor vessel or the leakage of iron, or is there some other cause for these problems?????:handshake