MBP 13", early 2015, 1TB SSD (366GB free), 16GB Ram.
I have exactly the same problem upgrading from El Capitan to Sierra, but it persists now after rolling back to El Capitan (10.1.6) with a TM restore. I have worked for several days with Apple Support, but no luck yet, so asking here.
I have 500GB Photos library (with 105k photos), backed-up to an external disk with TM.
I was able to work with the library just before doing the upgrade to Sierra. I did a TM back-up just before upgrading to Sierra. In Sierra, I tried to open photos, it said it had to update the library, but that got stuck, saying photos had "run out of application memory" and I had to force quit. After the failed update, it said I have to repair the library, which always stuck at 93% (and had to be "force quit") I tried it many times, after restarting the machine, resetting the PRAM, even in safe mode, but each time when I started photos it had to be repaired and it stopped at 93%.
We finally decided to roll my mac back to EL Capitan with my TM backup. That worked (took about 10 hours) but the photos library, which worked before with El Capitan, still needed to be "repaired" and again stopped at 93%.
What is strangely similar to the Jules Gray post is that no matter which back-up of the photos library I restore (I have about six on my TM backup drive, all previous versions of my photos library, about one TM backup a month), they all need to be repaired and all stop at 93%.
What happens at 93% (or 95%) of a photo library repair? What is it repairing at the end? Is there a way to override that ?
I am trying to figure this out because I was working on a photo book, and I have about six completed photo books I don't want to lose.
I did create a new photo library (in the restored El Capitan) and imported (almost) all my masters into it, and that does work, but of course all the faces, the moments and the projects, especially photo books are not there, and everything I read or hear says that I cannot recover those in a new library.
So my backup seems to be fine (rolled back to El Capitan). My repair stops at 93% for any restored photos library.
Is the problem in the way TM restores some files? Or is it a bug in the "repair" in Photos? OR is there some rogue or naughty file in my old photo library, that Photos tries to repair at about 93%, and it doesn't know what to do with?
I used to program. If I could I would put in some flags and see what is happening at 93% of the repair.