Edit: this is the deal breaker, which was denied to the Society lay time documents were brought to them for signing.
[Rorate Caeli] Abp. Pozzo, Secretary of the Pontifical Commission Ecclesia Dei, spoke to the semi-official daily of the French episcopate, La Croix, on the relations between the Holy See and the Society of St. Pius X, and among other relevant things said the following:
"The difficulties raised by the SSPX regarding Church-State relations and religious freedom,the practice of ecumenism, and the dialogue with non-Christian religions, of certain aspects of the liturgical reform, and of its concrete application, remain the object of discussion and clarification, Abp. Pozzo [of the Pontifical Commission Ecclesia Dei] added, but they are not an obstacle for the canonical and legal recognition of the SSPX."http://rorate-caeli.blogspot.com/2016/04/main-vatican-ecclesia-dei-official.html?m=1