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I think that if the areas stitched together have contrast differences induced near or at the edges, you need to get the exposures to be uniform, in point of the area that is stitched or the area that is at the edge.
Oddly enough, this might be a matter of choosing where those 'edge,' or stitched, areas are, as well as of the exposure being uniform ... if you were photographing bushes and other darker foreground objects against a background of dried grassy field, for instance, having the dried grassy field being where the various exposures or individual pictures were stitched together, would help a lot.
Because, with a uniform exposure *and* that exposure being of a uniformly one-toned or 'one-brightnessed' at the edges that are stitched together, a likely similitude of adjacent portions of the different exposures would be achieved. Try it, at an rate. (This might possibly be done simply by cropping some of the photos before stitching, as well as setting to one exposure level on Manual, as well as choosing the right framing for each exposure.)