Photos & Video Transferring in Portrait Mode

I've just upgraded my MacBook Pro (early 2015) to Sierra and my iPhone 6 to v10. Since I've done this, all of my photos and video are converted to portrait mode upon transferring from the phone to Photos 2.0 on the MacBook Pro (i.e., pics and videos are turned 90 degrees clockwise after taking them in landscape mode). Each picture has to be manually rotated, and videos have to be exported, rotated and re-imported since Photos is unable to edit them. To make matters worse, after you rotate pictures in Photos, they no longer expand with a double click from the thumbnail view.

Has anybody experienced this? I've not been able to find any similar threads and am getting very frustrated!