Floating Neutral is because of its connections with the Ground. It either gets loose and sometimes even breaks, which makes the Neutral to float. This can happen any where from electricity board to your final terminations. Primary cause is due to rust, corrosion, or a mechanical stress.
It’s a serious problem as the NEUTRAL balances the voltages between 2 phases.
Due to this faulty NEUTRAL, the 0V reference no longer exists. Which in turns makes the voltage out of balance, so some of your appliances may draw less voltage than they should while others draw more. And, you might feel flickering lights. And, in some cases, the power outlet/socket could malfunction, which might damage your devices and pose a fire hazards.