the problem is that you may have solid credentials and strong desires to hold a "lead" position in the group, so that you could earn the visibility and exposure needed to take over your boss's position later. However, the position may only be a supporting role in nature (my guess) and it does not offer the career path to grow into a management role.
So, everytime you complained that the JD is not clear or Boss's expectation is not clear, the actual disappointment is that this position did not provide you with a a chance to advance.