At the beginning of the year, Benefits in Payroll get zeroed out when benefit is based on a Plan Year

In SL 2015 and 2015 CU1, when a benefit is based on a plan year and the year rolls over, the Last Close Date gets zeroed out which causes the benefits to be zeroed out after the next check run.

This was reported as bug 36490 and there is a hotfix which can be located at the below link:  https://mbs2.microsoft.com/Knowledgebase/KBDisplay.aspx?scid=kb;en-US;3142492