It can be due to your battery is heating up too much and when the battery heats the charger through smaller volts due to which battery takes long time to charge. Charge it in cool place and make sure that battery is cool before plugging charger.
"The issue which has occurred in your device requires binary updates and the same is already escalated to R&D team for rectification. Soon you will get binary update for the same via FOTA. i.e. Menu> Settings> About Device> Software Update> Auto Update> Enable it."
