When you create user or group in Azure AD it is not immediately available in Sharepoint Online. I wrote about this problem here: Problem with delayed propagation of Azure AD groups to Sharepoint Online. In this post I will describe another interesting problem which may occur because of this delay.
Azure AD group members and owners may be retrieved with Graph API and with Rest API:
Graph AP endpoint:
Rest API endpoint
where instead of http://example.com you need to use url of your Sharepoint site.
The problem is that until Azure AD data won’t be fully synced to Sharepoint Online Rest API may return not correct data. E.g. /members endpoint may return actually owners, while /owners endpoint may not return users at all. Depending on how fast MS data center will propagate changes it may take up to several hours. So be aware about this problem.
The main advantage of Rest API endpoint is that it returns members count. While in Gtaph API $count query string parameter is not supported for users and groups: Use query parameters to customize responses:
Note: $count is not supported for collections of resources that derive from directoryObject like collections of users or groups.
So you may want to use Rest but notice that it may work incorrectly first several hours.