Currently users are unable to migrate all their photos from Photos to Lightroom since many formats are not fully supported such as Live Photos. Live Photos can be visualized in Google Photos so it does not look like it is an Apple issue... Please add full support for Live Photos.
I have just migrated to LR CC but lost 4000 Live Photo elements, a real shame this is not supported at all. I support adding support in the library, plus support to capture Live Photo’s in the in-app camera.