When doing a pano merge of several files taken with a Phase One IQ3 100 back, the merge is always in the wrong orientation. I have tried merging several horizontal panos, and LR always creates a vertical pano. After merging I can use the rotate tool to obtain correct results, so the issue isn't serious, but it is a challenge to evaluate the pano when it's vertical, since it is much smaller due to the limit of the screen height.
Updates to Lightroom Classic CC (8.2), Lightroom CC for desktop (2.2), Lightroom CC.Mobile (Android and iOS) were released on Monday, February 11, 2019. Please verify that your issue is fixed by the current update.