Dr. duan has diagnosed her client with bipolar disorder. dr. duan refers her client to new a therapist after the client moves to a distant town. the client's new therapist diagnoses the client with major depressive disorder. this lack of agreement between the two therapists who were evaluating the same behaviors would be considered

I believe the answer is:  low interrater reliability

Interrater reliability refers to the baseline score that agreeed upon by raters when evaluating a certain consensus. The conclusion with low interrater reliabiloity tend to not be seen as valid and might cause confusion if the raters are working for the same client

the answer would be in this answer. someone already asked the question.