User has checked the option Show account summary at the bottom of invoices, but the invoices still do not show the account summary.
This happens because the Global Settings option only applies to the new projects you create and not to the existing ones. For existing projects, you need to check the project rule Show account summary on invoice so that their invoices show the account summary. Check the Core Help for more on this rule. You might also want to check out this article: Global and project-level rules.