If you're not seeing any assets from a particular account, please ensure that an IAM Policy has been configured for the account in question.
If the IAM Policy and Role/User has been configured successfully then your account should be in a 'Healthy' status (or 'Warning' if certain permissions are not present).
If you're not able to see a specific subset of assets from a particular account, please check your IAM Policy to ensure that permissions are present for the assets in question.