Packer does a great job of managing and cleaning up the resource it uses, but it can only do that while it is running.
If your Packer job aborts for any reason (most likely network issues) then there may be some resources left orphaned, or unmanaged. It is good practice to check for any Packer instances (they will have Packer in their name), and stop them if there are no active Packer jobs running.
You may also need to clean up any leftover key pairs and security groups, but this is less of an issue as there is no cost associated with them (unlike instances).
