We once did this with a community member who would swing between being very helpful and particularly difficult. We scheduled a call (I took it with a colleague), and we ended up talking for close to an hour. Much to our surprise we learned that she used medication against depression and paranoia, and when she was off-meds her behavior would quickly deteriorate. She apologized profusely and suggested that we’d send her a private reminder whenever this happened again. This completely solved the issue and turned her into a loyal supporter.
Of course, this was a scary move, it will not work for all kind of trolls and it does not scale, but I thought the story illustrates that sometimes the situation is not what you think it is - a little ‘real’ contact can really help you understand the issue and find a solution.