You notice the error “Throttling limit reached, stopping migration” in the user migration logs.
As explained elsewhere, Google has its own throttling limitations which means you can only migrate between 2.5 and 3.5 GB of data within 18-24 hours per user.
Cloudiway automatically stops the migration of a user when this limit is reached.
There is nothing to do: this is expected behavior.
After 18 hours, the migration of a pending user is automatically restarted.