I have this issue on our SQL2008R2 SP2 instance.

It just didn't register any deadlock data in system_health for the last 11 days ( and counting ).

To fix it I request down time to bounce the instance :-$

btw:

SELECT * FROM sys.dm_xe_sessions;

addressnamepending_bufferstotal_regular_buffersregular_buffer_sizetotal_large_bufferslarge_buffer_sizetotal_buffer_sizebuffer_policy_flagsbuffer_policy_descflagsflag_descdropped_event_countdropped_buffer_countblocked_event_fire_timecreate_timelargest_event_dropped_size

0x0000000080D84081system_health0314415870043247610drop_event1flush_on_close0002015-03-20 06:12:13.5100

dropped_event_countdropped_buffer_count both have a count of Zero !

Very strange is that it states the create_time =2015-03-20 06:12:13.510 which is in the future !!! ( almost 3 days ahead)