Hi @Abhishek Mehta , please make sure that custom app mapping attributes are correct. This thread goes into detail on that. For example, one solution to this problem we've encountered before where the custom app mapping attribute mail was setup to take the attribute primaryemail. However, users created from Azure AD or coming from a local AD don't have the mail attribute assigned.
To fix the issue, we changed the mail attribute to UserPrincipalName from the mapping which uses the user email address.
Please let me know if you have any questions! If this answer helped you, please mark it as "Verified" so other users may reference it.
Best,
James