" However, a sense of continuing hopelessness remained long after depressive symptoms lifted."

I'm having a hard time just processing this sentence.   I've only recently had experience with depression (as a result of the serious illness of my wife)  but I cannot imagine what you (or the original authors of the study) could possibly mean by mood improving but still feeling hopeless.   To me a feeling of hoplessness IS a mood.

Could this just be a semantic side effect  of the way they set up or worded the questions in their study?   One of the big problems with psychology (when I was an undergrad I switched my major from psychology to neurophysiology because of this problem . . . ) is the reliance on subjective self-reporting which is confounded by the way words are interpreted, question order and association, etc.