I have a 2017 Macbook Pro and a 2018 Macbook Pro. The target machine has a bigger SSD than the source, so I know it's not a space issue.
I ran Migration Assistant on both machines and the process completely relatively quickly. After it completed I received about 2 dozen files that could not be transferred. The machine than boots into macOS and I start receiving repeated authorizations requests to repair files.
I also receive notice that the keychain needs to be replaced with default.
Should I attempt to boot the source into target disk mode and transfer via thunderbolt?
Best Answer
It sounds like your Migration didn't work, even though you didn't get error messages saying so at the time.
I always use either Target Mode or an external disk when I use Migration Assistant. I also don't do the Migration until I've gotten the new computer completely up-to-date, etc. I create an extra "Admin" or other dummy account which I delete later.
I would reset the 2018 MBP, create a dummy account, do all the updates, and then when the system was running perfectly, then I'd start the Migration Assistant using the 2017 MBP in Target mode.
The other thing I do, because it didn't work correctly once when I did it a different way..... After selecting the source disk, MA will scan the source and identify the files, accounts, apps, etc. that need to be transferred. Since I was transferring everything, I didn't wait for it to calculate the sizes of all these different things, and just said "Go" or "Next" or whatever to get it started. That didn't work. So, now, I always wait for the scan of the source disk to complete. I wait to see the size of the Users folder, the size of the Apps folder, etc. before I start the Migration.
Good luck!