mobile heats a lot while charging the device, it heats a lot also in slow charging, while playing games or using mobile it's ok, but while charging it heats a lot to extreme.
Slow charging and scheduled charging is broken and not working on .58 firmware. Use 2A wall charger if you do not want your device to heat up.
Go to setting => About => Software information.
If not already on .58 update your phone first, a little heat is normal during inbox 30W charger. Also, have noted your feedback.
@ARP_ASUS firmware is . 58 update only, i switched on slow charge option then also it show hyper charge, it doesn't even charge slowly, then what is the use of slow charging? see the screenshot it's hyper charging.