Vivo nex dual screen notifications

[DPzINSANITY]

Hi,
I have a Vivo nex dual screen and when I charge it during night (with an alarm set), It's like the phone kill all backgroud app until I unlock it. I have noticed it with whatsapp, if I just turn on the sceen on there isn't any notification (apps from google play store, notification from vivo apps or system are here) and when I unlock it, the notification appears, my friend have send a message in the night and from his app the message was sent but not recieved.
Anybody know what I have to do for these notifications ?

 

[Saloei]

I have the original NEX-S. Three things come to mind:
1. Settings\Battery\High background power consumption\ Locate Whatsapp and enable setting
2. Settings\More Settings\Applications\Installed\Whatsapp\Permissions\Single permission settings\ Enable Autostart
3. Settings\More settings\Task timer\Scheduled power on/off => OFF