Ok There are two levels to the practice of shunning by the JWs.
The one that most people are familiar with is when a formal announcement is made from the platform when a person is disfellowshipped or is disassociated and no one is supposed to talk to them. It is an extreme form of discipline supposedly meant to teach the disciplined one a lesson. The announcement is made to warn others that this person is a serious threat to your spirituality.
The second level can be split into two forms. The first is that a formal announcement is made from the platform that a person has been disciplined. "marked". People are to view this person as a threat to your spirituality. Relationships with them should be limited to spiritual activities like meetings and service if they are allowed. Hanging out with them at the local bar wouldn't be a good thing.
Then there is an informal "marking" that goes on. Based on what people see or know about a person, and what rumors they have heard some JWs choose to "mark" a person as a spiritual danger. Depending on what they believe they may simply "mark" as person as a minor danger. But they could take that to another level and treat a person as a serious threat and apply the rules of total shunning.
And it is this informal shunning that happens where the person is rarely if ever given a reason for the treatment they get. You pretty much have to guess and live with their choice.
My opinion is that these people have little to offer in the way of helping to reestablish the relationship.