Do you try to connect to Exchange online then use the command below? Which contained in this part: Prerequisite steps in Exchange Online I would suggest follow this part have a check on your Exchange online:
Get-MigrationBatch | ?{$_.MigrationType.ToString() -eq "PublicFolder"}
If you cannot find the failed migrated request, you could open a service request(for free) to Office 365 team help you check whether is there exist invisible failed migration request.
You can also try to change the Office 365 group email address, then check whether could migrate successfully.
I also want to confirm with you that did you try to use a new batch migration name for new created migration request?
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