Many oppo users are geting notification issues and they are looking for solution , Oppop users are not getting notification from Whatsapp News app at right time , sometime it is stucked in between and you need to take measure to trouble shoot this issue and you can do this simply in few steps
Oppo Phones Whatsapp Notification Problem
Start whatsapp, From home open Settings > App management and in the “Running” tab you will see whatsapp. In padlock icon, press it and it will turn green. This locks the app in memory and prevents it being closed automatically to save power and memory.
Try this setting hope that works.
Check all the security and power saving settings. The phone will freeze apps in the background or with screen off to conserve power,OR Go security center and turn off the”data saving”function.