The EPO announced the https://forums.epo.org/unavailability-of-most-online-services-from-27-to-31-december-7972 :
Due to technical maintenance work, most of the EPO’s online services (OPS included) will not be available between 12.00 hrs on 27 December 2018 and 08.00 hrs on 31 December 2018 CET.
For more details, please read the notification available on our website: https://www.epo.org/service-support/availability-of-online-services/2018/20181212.html.