This is FYI in case any one else encounters the same problem I had.
My daughter's Mac and iphone were using a common icloud account that had been set up for the family some time ago. She had lots of pictures stored in the icloud via Photos. We decided to set her up with her own icloud and itunes account recently.
The first icloud issue was in disconnecting her from the old account. The message that you'll lose photos and videos that are not fully downloaded to the Mac scared us for a few days as there's no simple way we could find to determine in advance which photos and videos were not fully downloaded. So we tried for those few days to download all of the photos and videos but didn't seem to make any progress. After a few days we gambled that we could continue with disconnecting and risk losing the photos and videos as they would still be in icloud under the old account. Then we saw the next screen which told us that we'll only lose 3 photos and 1 video - too bad that screen didn't come up earlier. So we disconnected.
The second icloud issue came after we connected to the new icloud account and tried to get her Mac photos to sync up to the icloud photos. We spent 2 or 3 days waiting for them to update and 2 separate calls with Apple support but no resolution. There were two additional things I noticed: 1) the iCloud Photo Library update bar (under Photos/preferences/account) remained blank (i.e, no green progress bar) for 2 or 3 days indicating no progress was being made, and 2) next to the heading "iCloud Photo Library" was the message in red that I had 29 (then 28, then 27) days to download my photos from icloud before they were deleted. This made me suspicious as it was a reference to the photos under the old account and I was logged in to the new account. So today, I gambled and disconnected from the new icloud account and again got the same message that 3 photos and 1 video would be deleted, which I accepted. I then signed back in to the new icloud account, got informed that I had too little space on the new account for all the photos and videos to be uploaded, I opted for more (paid) space, finished connecting, then went in to Photos/properties/account and viola, the iCloud Photo Library update bar now gives me 1) a count of photos to be uploaded and 2) green in the progress bar.
So, to summarize:
- If you're worried about losing your photos (or other files) if you disconnect your icloud account, be aware that 1) you should be able to recover them if you reconnect to the account and 2) that there's a subsequent window that will tell you how many you will lose (though it doesn't tell you which ones), and
- if syncing gets stuck with no apparent progress being made (especially no count of how many are to be synced and/or no "green" progress visible) then a possible solution is to sign out then sign back in to your icloud account.
