In this study, we employ 4D Scanning Transmission Electron Microscopy (4D-STEM) to investigate the relationship between image contrast, convergent beam electron diffraction (CBED) patterns, and local lattice distortions near dislocations in 2H-GaN. Our findings reveal a pronounced anisotropic spreading of the CBED pattern, which correlates with the local distortion of atomic channels and, therefore, with the direction of the Burgers vector of the dislocation. This behavior is a consequence of electron beam channelling perturbation caused by low-curvature channels. Thanks to the 4D-STEM capabilities, an accurate analysis of the localized CBED patterns around a screw dislocation reveals that the characteristic two-lines contrast observed experimentally arise mainly from an angular redistribution of the coherent diffracted electrons reaching the annular detector. The enlargement of the diffraction pattern develops in opposite directions on the two side of the dislocation because reproduces the local bending of the channels. By exploiting this directional de-channeling, we demonstrate the ability to determine both the Burgers vector and therefore the character of dislocations in a well-aligned zone axis configuration. These results highlight the potential of 4D-STEM as a powerful tool for atomic-scale defect characterization in semiconducting materials.