CathInfo.com

Receiving Holy Communion is “the most radical call to holiness” that any person can encounter, the Bishop of Shrewsbury will say in a pastoral letter this coming weekend.
Bishop Mark Davies will warn them against viewing the Blessed Sacrament in terms of “secular inclusiveness” as this diminishes its true significance to little more than a “token of our hospitality”.
Catholics must realise instead that through the Real Presence, the gift of Christ’s Body and Blood is the means to become the saint each of us is called to be.
Holy Communion restores strength to the faithful, breaks disordered attachments, separates Catholics from sin and helps them root their whole lives in Christ, the bishop will say.
Catholics must also repent of any mortal sin or lifestyle which contradicts their calling as Christians before they can receive Communion, Bishop Davies will remind his diocese.
“We see why we can never approach Holy Communion casually, still less if we have not confessed and repented of any mortal sin or of a lifestyle in contradiction with our Christian calling,” the bishop will say.
“The Apostle Paul urged the first Christians to examine themselves carefully before receiving Holy Communion because anyone who did so in an unworthy state would, he said, be ‘guilty of profaning the body and blood of the Lord’.
“The Church calls us to frequent Holy Communion, prepared by the Sacrament of Penance and Reconciliation so that we might become holy, might become saints. The Second Vatican Council urged us to ‘frequent’ both these two Sacraments eagerly and devoutly as the path to holiness.”
“Let us ask ourselves how we seek to receive Him with the deepest reverence and love, and how we spend the precious moments after receiving Holy Communion,” he will add.

http://catholicherald.co.uk/news/2018/04/02/receive-communion-lifestyle/

Where does he explicitly say that fornication is not a mortal sin?

Understand what he's doing in Amoris Laetitia.  He's saying that something which is objectively mortal sin can now be venial sin if someone discerns it away ... i.e. can rationalize it to himself.

Understand what he's doing in Amoris Laetitia.  He's saying that something which is objectively mortal sin can now be venial sin if someone discerns it away ... i.e. can rationalize it to himself.

In order for a sin to be mortal three things are required;
grave matter ( fornication is grave matter)
free consent ( that would exclude rape)
knowledge (It is understandable that there are some people who do not understand the gravity of this sin. this lack of comprehension could mitigate the culpability for this act. That would be true even prior to Vatican II.)