First, Sanders lost Nevada because Hillary Clinton won the caucus.
Then, the Sanders campaign put their ground game into effect, in an effort to overtake Clinton during the nearly-unique-to-Nevada process that allows for changes in pledged delegates at later caucuses. But he didn't get enough delegates to achieve that. The Sanders campaign does get credit for getting more delegates than they had before, of course.
Then, at the State Convention, Sanders had enough delegates in place to gain a couple of more delegates and possibly tie with Clinton in the end. But the organizers for the Sanders…