Looking into it, I can see some issues with the idea (I don't understand how it wouldn't fall pretty to the tragedy of the commons), plus I definitely don't think Sanders would fit into there. I don't see any of his proclaimed positions fitting into any definition of left-libertarian. Plus I don't see how left-libertarian wouldn't fall prey to the same problem we have with capitalism now, despite being an anti-capitalist notion. It's strong sense of individual ownership of anything other than natural resources seems at odds with a lot of other socialist concepts. I will caveat all of this with saying I have a very limited understanding of left-libertarianism, but just reading any given definition just seems to give rise to very clear contradictions. I feel like either it is problematic or no one is really sharing good definitions of it.