After installing the Feb 2018 update yesterday, portrait movies imported from my iPhone (6S) are strangely rotated 90o to landscape orientation. Previously, no problem with such files.
As part of my weekly collation of images from my phone, I export originals from Apple Photos, then import them into Lightroom. The specific files I am now having problems with, but didn't have before, are portrait movie files that are part of "live photos". The associated jpegs from live photos are all rotated correctly, and landscape "live photos" have no problem.
I tested and this extends to all portrait movies, not just the .mov parts of "live photos". The problematic imported .mov files look fine in Quicktime and Finder.
Lightroom Classic 7.4 was released today and should address this issue. Please update your Lightroom to the latest version and let us know if you continue to see the issue. Thank you for your patience.