The edge that appears in the panorama after HDR processing in Affinity seems understandable to me. Affinity does not "know" that this is a panorama. In HDR tone mapping, various automatisms run to copy the layers into each other. Then the content of the left edge may well be a little different from that of the right edge. And then it no longer fits.
The solution is to switch off the automatic tone mapping. In the opening dialogue where you import the exposure layers, at the very bottom is "Assign colour/tone values for HDR image". There you have to remove the tick. You can edit the resulting image with many parameters via the "Develop Persona". This applies to the entire image and thus avoids nuance differences at the stitch edges.
