Come together, right now, but then wait and don’t say anything
When the child is dysfluent, the listeners (usually Mom and Dad, and frequently extended family and friends) should wait patiently, no matter how long it takes, and then respond positively to the child's verbalization.
No verbal comments nor body language signs should be made in the presence of the child to indicate concern or dissatisfaction with the child’s communication skills.
Parents, furthermore, should run interference for the child and ward off any derogatory comments by other children, teenagers or adults in front of the child.
For example, it is very natural for others to mimic the child's dysfluency.
Eventually, maybe in months, the dysfluencies will subside as mysteriously as they came.