Assume that you have AlwaysOn Availability Groups configured in SQL Server 2014 or 2016. If an application uses the TABLOCK hint, the Service Broker Usage Control Service (UCS) task leaks memory. In this situation, you can see that the number of tasks in the sys.dm_os_tasks function continuously grows. This causes AlwaysOn synchronization to become slow.
This problem occurs because the UCS task leak may cause Lock Monitor to consume more CPU usage.
This problem was first fixed in the following cumulative updates for SQL Server:
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.