Microsoft released Exchange Server 2013 CU14 in september and issues that are being addressed by Exchange 2013 CU14 are listed here. Along with Exchange server 2013 CU14, Microsoft also released CU3 of Exchange 2016. Implementation of these updates in production has caused issues with database content index failure. Both the updates were released in September of this year.
I have experienced this issue with Exchange 2016 CU3 implementation and a lot of customers has reported the same issue on Microsoft TechNet forum as well for Exchange Server 2013 CU14. Working with Microsoft support ticket, it has been reported back that a bug has already been acknowledged and for now, the solution is to deploy a new Exchange server 2013 CU13 or Exchange Server 2016 CU2 and move all user mailboxes to new server. Although, it’s the ugly workaround but for now we have to do this or I would say, we shouldn’t upgrade our Exchange implementation to current CU until a fix is being released by Microsoft.