I'm also running into issues trying to align outcomes to New Quiz questions, similar to but not exactly what you described here. Rather than create a new topic, I thought it might be beneficial to add my experience here to compile various New Quizzes/Outcomes issues for Canvas to review.
I created three Outcomes at the institutional level, then created an item bank at the institutional level with 6 questions, and aligned them to their appropriate Outcomes (2 questions per outcome). In a test course, I imported the three outcomes, then created Quiz #1 and used all 6 questions from the item bank. At first, the Outcomes > Alignments page showed them correctly: 2 alignments per outcome (both questions attributed to Quiz #1).
However, when I created Quiz #2 and added the same 6 questions from the item bank, two of the Outcomes on the alignments page were still only aligned with Quiz #1 (nothing for Quiz #2), but the third outcome was split (1 question aligned with Quiz #1 and the other question aligned with Quiz #2). While trying to fix this third outcome, the two alignments for the first outcome suddenly disappeared! I hadn't touched either of those questions. I've waited and refreshed the Alignments page several times in case there was some delay in them showing up, but it's still wrong. Is it not possible to re-use the same outcome-aligned item bank questions in multiple quizzes in the same course?