this is a bug... this notification only appears when the battery is already 80% or over, which is pretty stupid because at that precentage the phone is way more cooler when charging.
If you have a 20w charger pay attention when the phone is arround 25-65% charged, it will get pretty hot if you are using 20w charger, but NO OVERHEAT notifications and the phone just kept charging..
Then at 80% for no reason at all, this "Charging On Hold" notification appear when the phone is way cooler compared to when it is 25%..
Good thing is this bug most likely will be fixed on 16.2. im using 16.2 beta 3 and no longer getting this charging on hold notification