Like i said, the chain has to be a certain density AND STIFFNESS. Try it with a sisal rope, it won't work.
It's no different than throwing a ball into the air. You impart enough force to overcome gravity. The momentum of the moving mass of chain imparts enough force to over come gravity (for a bit).
2 scientists in 2014 tried to explain it and is still open to debate !!
https://royalsocietypublishing.org/doi/10.1098/rspa.2013.0689
