Cloudiway migrates Google Apps mail using the IMAP protocol for which Google imposes throttling limitations.
Reaching the limit triggers a safeguard that temporarily suspends the account.

See https://support.google.com/a/answer/1071518?hl=en

Typically, Google allows a download of between 2.5 and 3.5 GB of data per day after which it may disable the user account for up to 24 hours.

Cloudiway is subject to this limitation and migrates only up to the limit of data per day.
Once this volume of data is reached, the migration is put in Pending status and automatically restarts 18 hours later.
Therefore, a migration of a 10-GB mailbox may take up to 3 days to migrate.