One of the biggest problems phones OnePlus is refraining from sending notifications and cut the internet connection when entering the device the phase of deep sleep until the user wakes him again.
To improve the precision, this is not a problem actually, where the developed interface of Oxygen preparation of withholding notices and the internet after a period of non-use the device for longer battery life.
Those default settings can be disabled by going to Settings > Battery > Battery optimization > improvements to the advanced, where you will find two options you can give them a list of “improvements ahead”.
Improvements deep (Deep optimization): this setting is not recommended to modify it only if you experience loss of internet connection or close the apps running in the background.
Improvements to standby (Sleep standby optimization): this setting is recommended to be amended in the case of late notices; the works with the preparation of fortifications deep in the default mode on the cut the internet connection in the case of deep sleep in order to prolong the battery life.
Since that disabling these settings may adversely affect the battery life, it is recommended if the notifications that come from the delay necessary.