It implies that someone has soft cheeks. Mochi is used to refer to a cute person.
It is a popular adjective and it's not exclusively a nickname for BTS' Jimin.
church hurt is where you experience a degree of distance, pain, or judgement from your church community. Essentially, you are just unable to “find your place”. This is prevalent in the Christian community, but can be extended to other religions.
Now that I am an adult I am beginning to heal from the church hurt that was inflicted on me as a child.