Ok.
1st check your holiday calendar and WSR for this period. After that check what is the day type and holiday class is assigned against Christmas Day and New Year. If all are in correct place then check the custom PCR which is used to accumulate the hours and also share the details of WSR(PWS from 20.12.2015 to 02.01.2016) and this custom PCR.
Regards,
Sankarsan