Thanks to everyone who has posted some solution or idea here; I think ALL of us appreciate the efforts of the "few" - it is obvious Apple is not willing to make the effort, so we have to reply on others here. I have some updates to share on this issue and believe it is worth the time for everyone to read. APPLE...it is WORTH your time to read as well, it MAY actually help!
I struggles with this sync for the last several months and finally was able to do a drastic check on it. While this issue was a big factor for me, the bottom line was I had both an older iPhone and an older laptop...I WAS due to update them, and I did! So after getting a new iPhone X, AND a new Lenovo X1 Carbon laptop, I was looking forward to getting back to normal! I knew better than to set up either piece of equipment via a backup of the older one; so both the iPhone and the laptop got fresh new install/setups done on them. So here are the specs:
NEW iPhone X 256 (setup as "new phone")
NEW Apple cable
NEW laptop
NEW install of WIN 10, iTunes
ALL updates done and current.
I did a couple of test syncs without photos. They were done instantly,as I expected. I added in my playlist; it was slower, but I expected that as it first time copied all my music over; second pass was again, instant. Now to add in photos. I did it with only ONE folder to be synced (120 photos)...it worked, fast too! Added in a couple of other folders and the same thing, it was going great. I was happy, and thought I had it solved, at least for me, so I clicked all the photo folders I wanted synced and let it go. It was naturally slower as again, 1st time copy of all those pictures, but again, it WORKED. Well, it worked once anyway. Subsequent syncs have ALL failed....stuck forever on "reading photos..."
I am afraid all that advice about hard resets on the phone, uninstall and reinstall software, new cables, dif ports, etc, etc, etc.....just does not work. All new equipment with NO other software or apps installed, repeated the problem over and over. For the record, LOVE the new iPhone, works amazing, but as my iPhone 6 was NOT the problem here, i cannot help but being "taken"...again!
Also, I think a large part of the reason this is not getting as much press and attention is the fact that so many users do not even bother syncing to a PC, especially the largest user base in the younger generations. My 21 year old daughter has all Apple gear (iPhone, iPad, MacBook), they all use the same Apple ID; I have shown her, and some of her friends, how to have all devices synced, etc. Ya, they don't care! As crazy as that sounds, they just don't care. They take a zillion pics a month and do not care if they lost them all, and 99% of the time, they never look at that picture again after they take it - aka "SnapChat". Music? Again, who cares. They have 10 GB data plans, a 50 MB Internet feed everywhere they go so.....lose their entire phone data? Their answer is "I will just download it again". And they are partly right. They can re-consume anything digital, any time they want....
Hope this helps someone! It was a clean lab test for sure, Apple, you have to do the same. I am sure a few photos will most likely not repeat this problem, make sure you try with 3000+ photos (large file size photos, not a bunch of compressed low quality photos!