When farming Weeping & Twisting Vines, they will not re-grow after harvesting. I have a farm set up with pistons breaking the vines 1 block above the initial sprout. After placing the initial sprout, the vines will grow but once they are broken by a piston they will no longer grow. In offline game saves, vines appear to not regrow after being broken by player or another in-game item (like a piston). However, on Realms the vines will regrow if a player breaks them but not if a piston or other item breaks them.