When merging photos in LR Classic CC v8.0, the resulting DNG has all kinds of Tone adjustments added to it. I haven't seen this problem previous to this version. The merged photos have no adjustments to them. Photo is attached of the adjustments added:
When merging, does it have "Auto Settings" ticked in the box shown below? If you, untick it and try again(it will remember your choice). It's the same result as 'Auto' shown in the basic adjustment panel.