Are there Sins that Priest can’t absolve?
Yes there’s. It’s called reserved sins.
According to the Code of Canon Law in 1917, Reserved Sin is a term of Catholic doctrine, used for sins whose absolution is not within the power of every confessor ( Priest), but is reserved to himself by the superior of the confessor (Bishop or Pope).
To reserve a sin presupposes jurisdiction, and therefore only the pope alone can make reservation for the whole Church; bishops can do the same for their diocese only. For a sin to be reserved it must be mortal , external, and consummated.
Among the list of sins to be reserved is the sin of Abortion.
According to the Cathecheism of the Catholic Church (no. 2273) anyone who has an abortion, participates in an abortion, or supports an abortion, he or she, by the previously mentioned actions, is automatically excommunicated from the Catholic Church.
Consequently, that person can no longer receive any of the Sacraments of the Catholic Church, be it the Sacrament of the Holy Eucharist (Communion), Marriage or the Sacrament of Confession.
And for an excommunication to be lifted (ended), the sinner must get to the local Bishop, inform him of his/her “latae sententiae” excommunication through the sin of abortion and ask the Bishop to have the excommunication lifted (ended) and to be absolved of the sin of abortion.
However, the Bishop may authorize a priest to specifically deal with this absolution on his behalf. (C.C.C. # 1463) Contrary to the famous belief of Catholics, this does not mean that all priests can absolve a penitent of the excommunication. Only a priest who is specifically appointed by the local Bishop can do it.
Except, In danger of death any priest, even if deprived of faculties for hearing confessions, any priest can absolve a penitent from every sin and excommunication.
But to the Glory of God, Pope Francis has indefinitely extended the power of Catholic priests to absolve the sin of abortions. He made the announcement in an apostolic letter which was released on Monday (November 28, 2016) for the period of the Church’s Year of Mercy, which ran from December 8, 2015 to November 20, 2016.
The restrictions was removed in order to save a dying soul from a mortal sin.