We have recently identified a problem in October and November 2015 CU which will also be present in the upcoming December 2015 CU for SharePoint 2013.
These updates will cause outbound query federation to stop working. Outbound query federation returns federated results to SharePoint Server 2013 Search services when SharePoint Server 2013 Search services query the SharePoint Online search index. This issue will be fixed by the January, 12, 2016, cumulative update for SharePoint Server 2013.
If you rely on outbound query federation with SharePoint 2013 we recommend to wait for January 2016 CU for SharePoint 2013 rather than installing October, November or December 2015 CU.
See following KB articles for official information: