Bernie was fucked by the establishment stranglehold over mainstream media, inherent flaws in the primary system, and some truly underhanded tactics. There has been no good evidence of any kind of tampering with the votes.
Bernie has always been a pragmatist. The progressive movement has nothing to gain by him obsessing over sour grapes. Contrast that with Hillary who will live the rest of her life locked into the day she lost.
Libertarianism is properly a socialist philosophy, but it's been coopted by the far right in America who then started exporting their bullshit to the rest of the world. It's entirely possible for two people to call themselves "libertarian" and have next to nothing in common in their understanding of what that means.
Most libertarian support of unions in America is a bad joke. It's meaningless feel-good rhetoric that completely ignores the entire history of unions in America. Corporations have a million ways to crush unions and union organizers. Without government regulations requiring corporations to engage with unions, unions are next to impossible in reality. But that's just fine with the kind of people attracted to the Libertarian party, because they don't live in reality.