The high void content in laser-assisted fiber placement (LAFP)-manufactured thermoplastic (TP) hinders industrial adoption, with tape deconsolidation being a critical yet understudied factor. To address this research gap, this study provides an in-depth investigation into the deconsolidation mechanisms of TP tapes during the LAFP heating phase. A series of comparative experiments were conducted to systematically evaluate the effects of tape residual stress states (fiber-matrix combined, fiber-dominated, and near stress-free) and heating methods (laser vs. oven heating) on deconsolidation behavior. Deformation along the width, voids, thickness variations and surface roughness were identified as key factors to characterize deconsolidation behavior and to elucidate its underlying mechanisms. The results reveal that the matrix residual stress plays a dominant role in exacerbating deformation along the width, nonuniformity in thickness and intralaminar voids. Additionally, fiber decompaction—induced by the recovery of elastic deformation—contributes to surface deformation by generating voids near the surfaces. Furthermore, laser-heated tapes exhibit more pronounced intralaminar voids and higher surface roughness than oven-heated counterparts, underscoring the influence of heating rate on the release of residual stress. This study advances the understanding of deconsolidation mechanisms during the LAFP heating phase, and provides recommendations for optimizing the manufacturing of LAFP-grade TP tapes.