Why Does Samsung Mobile Device Stop Charging When Not Fully Charged Yet?

During wireless or wired charging, both the device and the charger may become hot. If the device heats up or the ambient air temperature rises, the charging speed may decrease automatically. 

If the battery is heated above a certain temperature, the device might automatically stop charging.

This is a normal operating condition to prevent damage to the device. Wait for the device to cool down and then begin charging again.