You are in a hybrid environment and custom attributes for users are not populated in Signature 365.
Custom attributes are not being synchronised from your on-premise Active Directory to Azure AD.
Completing the steps below will ensure custom attributes are synchronised from Active Directory to Azure AD:
- Open Microsoft Azure Active Directory Connect
- On the Optional Features pane, tick the Directory extension attribute sync option:
- On the Directory Extensions pane, add extensionAttribute1 (user) through to extensionAttribute15 (user) to Selected Attributes:
- Complete the wizard