Sounds reasonable to me. It looks like settling damage. I would patch it and see what happens as it will be obvious if it moves more. Maybe roots under it are rotting.
I am curious about something. A party wall has a specific meaning in building codes pertaining to buildings. Is that type of wall called a party wall in your part of the world?
I am curious about something. A party wall has a specific meaning in building codes pertaining to buildings. Is that type of wall called a party wall in your part of the world?