Only last tangents layer was written to all tangent layers before this fix. Code before fix evaluate tangents for all layers into mesh loops data (which keeps data only for one layer) and then writes information about 'each' layer which is actually only the last one. Code after fix evaluates tangents in the beginning of the loop that exports tangent data so that data for correct layer is being written into fbx. Co-authored-by: Andrey Zhitkov Pull Request: https://projects.blender.org/blender/blender/pulls/141839