What sort of problem is an adjustment disorder?

Reaction to problems. Adjustment disorder refers to problems with mood, behavior, or both, that arise directly because of an identifiable situation. For example, a child might abruptly become sad, withdrawn, and oppositional upon hearing that her parents are getting a divorce. Although it can be chronic, it usually has a clear beginning and may resolve if conditions change.
Behavioral/cognitive. I will refer this to experts in behavioral medicine, psychology, psychiatry. Thanks for asking this important question.