We have had confirmation from Microsoft that a fix is in the process of being deployed to affected tenants. Note that it is expected to take up to 8 days for this to be 100% deployed to all tenants. If you have been affected by this problem please continue to retry the migration to verify that the fix has been deployed. In the meantime we will provide any further information as soon as we receive it from Microsoft
Microsoft released an advisory earlier with further information (EX257082) and this can be downloaded from the following: https://bittitan.sharefile.com/d-s9150a59c5da74ef5a4a9a1fb8ce9b092
We will continue to provide further updates as soon as possible.