If users are unable to login it's typically due to their assigned role within the AuthHub Azure AD SSO application.
Check the AuthHub Azure AD SSO application within your Azure directory (This application gets created automatically the first time you setup the connection). Once you find the application, typically called "CloudHealth", click it and then click users and groups on the left hand side. This should list out individual users on the left, and their assigned role on the right (Administrator, power, or standard). If the impacted user is not in this list then be sure to add them and then assign the desired role. This should allow them to login to the platform.
This applies to AuthHub Azure AD configured with Azure Roles under Role Passing type: