Migration assistant

I have never looked at how much I've migrated, but I doubt it was anywhere near 400GB.

How are you transferring? Direct connected cable or Wi-Fi? If Wi-Fi, how fast is your router?

9 hours seems a bit long for any connection, but some people have old wi-fi routers.

I would. Try again. You might try running First Aid in Recovery on the old Mac to make sure it isn't some disk problem. It sounds like it is on that end.

I've always done Migrations from a Time Machine backup drive.

KJTemplin wrote:

It may be a disk issue as I tried it again and this time I canceled it after about 30 minutes of the same looking for files. I am now using my Time Machine backup and it is transferring the files. I should have done this from the get go.

Getting more than one computer involved in the thinking never seems to go well.

If you mean files stored in iCloud Drive, but not downloaded to your Mac, no. It copies what is in the source. Some files may exist both in the cloud and in your Migration source.

Probably should be done by now.