Chromatic abb. enable >> Manual defringe >> denoise(luminance) >> sharpness & Mask >> Adobe color profile(modern01, 02, 04… as you like)
The seam is already introduced with the removal of chromatic aberation. Using masking in sharpening perhaps adds to this. Both operations take the surrounding pixels into account which fails at the edges of equirectangular images.
You can work around this issue by applying these operations before stitching.