It shouldn't come as any surprise that, like other web host providers, A2 Hosting's unlimited plans aren't actually unlimited. It expect you to use its service like "similarly situated customers." This is like being on a highway. If everyone is going a few miles above the speed limit, you're probably okay, but if you're barreling down the fast lane past everyone else, you're probably going to be asked to slow down.
It is unwise to attempt to transfer a domain immediately before it expires. In some cases, a transfer can take up to 14 days, meaning that the transfer may not complete before the registration expires. This could result in loss of the domain name registration and failure of the transfer. To avoid this, end users should either transfer well before the expiration date, or renew the registration before attempting the transfer.