Sync Session Failed to Finish (May 2021 Edition)

Dear Amanda,

Thank You for picking this topic up. This time (after many trials and errors) I managed to resolve the SSF2F error by just deleting all my device backups (Manage Backups -> Delete Backup) and creating a new backup for each device (with the cable).

Another time before that, I had to use the Image Capture App and use the 3-dot (...) menu to switch the default app that auto-starts when a device is syncing with the cable.

Another time, I had to disable and re-enable iCloud Photos to resolve the issue.

Another time, I had to reboot all devices, go to Safe Mode (as You already mentioned), reboot again and the error was suddenly gone.

Now the SSF2F error is gone - until it will come back in one of the upcoming iOS and/or MacOS updates.

This is really frustrating as the Apple Hotline could previously never help in any of these cases.

The second error still persists:

After a clean MacOS reboot, wireless syncing works on all iDevices but after a certain amount of time, the Mac becomes unable to call out to any of the iDevices, so the wireless sync process is unable to start. And YES, restarting MacOS helps resolving this error, for a few hours only.

Issue could be resolved by applying the workaround:

Update to iOS to 14.6 & delete all local iOS device backups on the Mac.

@AppleThree: it has nothing to do with music syncing. The "Sync Session failed to finish" issue happens in the last step when the photos library is accessed.

Yet another, even more annoying issue is that sync over Wi-Fi randomly crashes macOS Finder on Mac mini. Reason is that the Mac min does not wait for the sync to complete and tries to go to standby, which then causes an endless sync-loop.

In consequence, when the Mac mini wakes up the next time, it does not go to sleep anymore. Finder is locked in this sync loop and cannot even be terminated. Rebooting macOS can resolve the issue, but this is difficult because Finder does not "let go" any more as it claims to be still in the middle of a syncing process.

It is a miracle to me how the Apple internal software QA is still missing those issues over the years. The issues are so easily reproducible when using the devices for a couple of days in a WLAN environment, where mobile devices are roaming and NOT staying in the network the entire day. I remember the old days when we had Catalina and less severe bugs in macOS Finder.

We can reproduce the issue on 6 independent iDevices (iPads / iPhones) syncing with two independent Macs, all with the latest OS installed. This is a mass-problem. The internet is full of reports about this error and if it were not an OS bug, there would be a sustainable solution in public already. One reason is for sure that some services do not properly re-initialize after waking from standby. A reboot will be the solution to almost anything - for some time. For that wisdom I don't need another two hour discussion with the L1-Support. Will be happy to talk to the C-Level to discuss potential root causes if sb. reveals their number.

Still not fixed in 11.5.1

Issue seems to be connected with the Photos Library: error appears after Step 6 "Reading Photos Library".

@Papa Smurf: it's also happening on all iPads, so the issue is not tied to cellular data being on / off.

Issue is not fixed with iOS15.1 I believe it is built-in macOS and has to be fixed there.

Dear Sharon, thanks for Your reply.

I can assure You that the SSF2F issue is not intermittent and that my cables are good.

It happens after a larger MacOS or iOS release is rolled out. We should not waste more time in trial and error testing, as the only people who will be able prevent recurrence are the programmers.

If You look out for "Sync Session Failed to Finish" on the web, You will find plenty of cases and as many solutions to try out, when you have the time.

It would help to find a meaningful error log on MacOS that could be saved as the error reoccurs to proceed with something that could help them fix the issue.

Fyi, the "Image Capture" App which is built in MacOS is capable of setting the parameter for "the" app that auto-starts when an iDevice is connected to the Mac with a cable. In most cases, the setting is "none" (no app starts). You can set this to "Photos" but the setting may become corrupted silently, causing additional sync errors.

MacOS 11.3.1 / iOS 14.5.1

Issue is still not fixed in MacOS 11.5.2

@papasmurf2021- Yes, it works. But the error will come back after some time. That is the reason why talking to the Apple Hotline makes no sense. The issue is solvable with trial-and error and eventually comes back after a couple of days. This is something only the C-Level can solve.