How to use Quick Connect for Cloud Services to synchronize Custom Attributes 1 - 15?
Those are not displayed by the Office 365 Connector and therefore are not available for synchronization.
For some connectors, the connector schema definition can be extended with a simple XML modification.
Please refer to Knowledge Article 71853 for details:
However, the Office 365 Connector does not support the schema extension method described in KB Article 71853.
Enhancement request number TF00331536 has been submitted to Development for consideration in a future release of Quick Connect for Cloud Services.