Unable to share photos from iPhone
When I view photos in the Camera app on my iPhone 6S Plus by tapping the icon in the lower left corner (Camera Roll?) and try to share (Air Drop, Mail, Message) some photos taken on a trip in April, I get a text box that says "Unable to share. There was an error while preparing to share. Please try again later." Of course, repeating the attempt from time to time over a period of weeks, I get the same message. This fault occurs with every photo on my phone taken before a certain point on that trip, and none after. The earliest photo that can be shared and the latest photo that can't were taken minutes apart. (There's one exception, a single video taken a week before the first photo that's shareable. And that video on the iPhone now appears out of chronological order, inserted into a series of photos taken a month later!) All of the unshareable photos and videos appear to display/play normally on the iPhone.
Then in the Photos Library folder in the Pictures folder in the home directory on the MacBook that I use with the iPhone, with the iPhone tethered and freshly synced, I discovered that there is an entire year of iPhone photos missing – starting in April 2016 and continuing to April 2017 with the earliest photo that I can share. (I acquired the current iPhone well before the start of this gap, and the laptop well before that.) I thought this was a clue to a fault that was causing both problems – but then I found that none of the photos that appear in the Photos Library taken prior to the year's gap can be shared from the iPhone either! Still more confusing is that, in the period prior to the 1-year gap, some photos that appear in Photos Library are no longer on my iPhone, the same one I took them on, and vice-versa. Some of these that are missing from the iPhone I may have deleted, but not all, and I think that would cause them to be deleted from the Library.
Clearly something is extremely screwed up, and I have no idea what, or how to fix it. And there are a few hundred photos on the phone that I want to get onto the computer for organizing into an album.
Suggestions?
MacBook Pro (Retina, 13-inch, Late 2012), OS X Yosemite (10.10.1), 500 GB SSD