Is there a term for a measure in which an extremely high or low score is considered bad?
I recommend looking at non-scientific writing describing when too much AND too little of something is not good-- when average/in the middle is best for a certain outcome. This is true in many aspects of life, so you'll find a variety of words that may express what you want to convey about these high-end suboptimal and low-end suboptimal scores. 

English StackExchage wordies may know an existing noun/adjective for exactly what you want. If there isn't a word to express what you mean, you're free to create one. Perhaps pairing the prefix "extra-" in the sense of "outside the optimal range", or the prefix "dys-" in the sense of "unfavorable scores" with word(s) relevant to the measure.