I would be concerned about the privacy of individual jurors who are experiencing the evidence or the process differently from one another and about the capacity to deal with some of the issues that were raised in terms of interpersonal conflict. If the stress is the product of a conflict, it may be that people wouldn't raise the issues in a group setting.
I'm not a therapist, so I don't know, but those are the sorts of things that would be of concern to me. We wouldn't want to create a situation that stigmatizes one juror in respect of the group by having them disclose what was going on with them individually.