A few more thoughts, are any of the images virtual copies? and how much overlap did you use. LR needs a good bit of overlap, at least to me.
Also I have found it best to do the pano merge before you work on the files with anything like adjustment brushes, or ND etc, as a lot of those will be dropped when the merge is done.
Are the files raw or jpg, as I have found LR does best on raws.
You might also try Ptgui, or Kolor or Adobe CC and see if you can get a solution from one of them. Both Ptgui and Kolor allow for demo periods.
Paul C