Failed transfer data from your old phone to your new iPhone (Quickstart, local Backup, iCloud backup) -> Solution

iOS 14.4.1

1. First I tried to use the "Quick Start" to transfer data directly from the old iPhone to the new iPhone.

At about 90% it failed with the error: "Data Transfer Cancelled, Reset iPhone to start setting up again."

The I followed each tip I could find in the Internet, why the data-transfer could fail:

a) place devices close to each other the whole time

b) strong WLAN-signal

c) fully charge both iPhones (reports saying charging-levels below 40% could mitigate the sync)

d) avoid/silence background activity on the iPhones - Settings > Battery > Low Power Mode

e) forced restart (both) iPhones ( see https://support.apple.com/guide/iphone/force-restart-iphone-iph8903c3ee6/ios )

f) reset network seetings ( Settings > General > Reset > Reset Network Settings ) !!! you will lose all your stored WLAN-password and have to re-enter them !!!

g) reset Location and Privacy: Settings > General > Reset > Reset Location & Privacy

h) delete all profiles (you only have the menu-point if you have installed profiles): Settings > General > Profiles

i) place the sim-card in the new iPhone (I don't know why this could help, but found one report indicating this as a possible source of failure)

Since none of the above given tips worked for me, I moved on to the next step.

2. I tried to backup with iTunes / Finder

(the plan was to restore the new iPhone from the local backup).

Connected to a MacBookPro with macOS Big Sur with all updates (11.2.2) and more than 3 TB free space, used original cable (USB-C Lightning)

The backup also failed at about 90 to 95% with the meaningless message "... because an error occured while reading from or writing to the iPhone"

Again I tried different tips found on the internet:

a) Encrypt local backup checked or unchecked (both did not change anything)

b) delete old backups (of different devices): rename ~/Library/Application Support/MobileSync/Backup to ~/Library/Application Support/MobileSync/BackupOLD

c) empty lockdown folder /private/var/db/lockdown/ (you will be asked again to trust this device when connecting iPhone to MacBookPro)

d) Used the free "Apple Configurator 2" (https://apps.apple.com/us/app/apple-configurator-2/id1037126344?mt=12 ) - in this program you can right-click on a connected device and backup from there. But since it internally uses the same routines as the normal backup, it fails with the same errors

3. Backup with iCloud

I had 90GB of data, so I bought the upgrade for the 200 GB.

Then I tried the manual backup (Settings > [your name] > iCloud > enable "iCloud Backup" > Back Up Now) (See https://support.apple.com/en-us/HT203977#icloud )

Now I had to wait for about 5 hours (100 MBit connection) to go to about 90% to finally fail. (By the way: the calculation of the remaining time is useless: I started at about 10 minutes - then it went up to 25 minutes and during the hole 5 hours it stated to finish in between 20 to 29 minutes...)

Same result: iCloud-Backup stopped with a message indicating that the backup had been interrupted due to network-problems (what I could rule out for sure!).

In a next step I selected single items to be included or excluded from the iCloud-backup. I had read, that especially items with "abnormal" characters could stop iCloud from backing up successfully. You should especially look out for geo-coded files, because they could contain special characters in the names of points, cities ... But how to find these files?

To disable or enable items to be included in iCloud-backup go to: Settings > [your name] > iCloud > Manage Storage > Backups > [your device] (> Show All Apps)

First I disabled a chinese-keyboard-programm - but to no avail. Then I decided to disable the largest piece (since iCloud Backup is slow) - I disabled the backup of the Photos.

AND THIS WAS THE FIRST TIME THE BACKUP SUCCEEDED!!!

SOLUTION

Since I didn't want to loose the photos, I tried to copy them to the harddisk of my MacBookPro. I didn't want them in my PhotosApp (Mediathek), since I have a collection of Photos there and didn't want to mix the photos. Therefore I decided to use the "Image Capture" App (Geman: Digitale Bilder) (See: https://support.apple.com/guide/image-capture/transfer-images-imgcp1003/mac)

I selected all files and a Download-Folder and clicked "Download All". The import failed after some minutes BUT:

THIS APP SHOWED ME THE CORRUPT FILES DURING IMPORT.

It just showed 5 files (videos) that could not be copied. So I deleted the files on the iPhone. After a second run - 3 more corrupt files were shown, that could not be copied. After deleting them, a third import could be run without any problems. Hope came back!

Because during all my tries a had figured out, that the local backup was fastest - In a first step a made a SUCCESSFULL (!!!) backup of the old iPhone to my MacBookPro.

In the next step I tried the direct copy from the old to the new iPhone using the "Quick Start" and it finished successfully !!!