Breaking news: the German Federal Constitutional Court (Bundesverfassungsgericht) has, according to this report, ordered the Federal President not to ratify the Agreement on a Unified Patent Court.
According to the report, this is due to a constitutional complaint having been lodged at the Court by a private individual, whose identity is not known at present.
It seems that the Court's order is, for now, a temporary measure pending a full hearing of the case and a final decision. Nevertheless, this development casts new doubt upon whether the Unitary Patent Package can enter into force prior to the UK's departure from the European Union (scheduled for March 2019).
Details are scant at present; further news will be reported as it develops.