I may be mistaken, but Cardinal Kasper may be correct here. Saying that it is licit for people in a persistent state of adultery to receive the Eucharist would be heresy. However, receiving the Eucharist in this state would technically be sacrilege.
This is formal, not material, heresy:
Popes letter to Argentine bishops on Amoris Laetitia part of official record
It not only would be a sacrilege, it would be a mortal sin for both the communicant and the priest, knowingly, administering the Precious Body.