Let me try to explain.
The customer is a big company (1000+ users in local Active Directory). Now they are using Azure more and more. The project I'm working on is hosted on Azure as an App Service. Now they want to enable all users to use this application. In order to do that we've developed some code which uses Graph to query Azure Active Directory (actually an app registed in AAD) and retrieves users based on name or e-mail (so they can be found and invited). The customer now complains that only limited subset of users is returned by Graph query.
I've done some investigation and it looks like the problem lies somewhere else. When I go to the Azure Portal to see all users in Azure tenant I can only see around 20 users. These are the users that can be searched through Graph. But I cannot see all these other 980+ users. I asked one of the users which was not visible in Azure Portal to login to the portal. When user did first login, I returned to the Azure Portal and voila - the user can be seen in Azure Portal and is findable through Graph query.
I hope you know what I mean?