If the first word of Paul’s hymn spoke of the need for a patience that does not immediately react harshly to the weaknesses and faults of others, the word he uses next – paroxýnetai – has to do more with an interior indignation provoked by something from without. It refers to a violent reaction within, a hidden irritation that sets us on edge where others are concerned, as if they were troublesome or threatening and thus to be avoided. To nurture such interior hostility helps no one. It only causes hurt and alienation. Indignation is only healthy when it makes us react to a grave injustice; when it permeates our attitude towards others it is harmful.
I might add that indignation is more helpful when our reaction is to an injustice suffered by another. For oneself, there is discernment on how to deal with wrongs suffered. The path is more sure when someone else has suffered.
Remember that Amoris Laetitia is online here.