If you like to save battery power with your Samsung Galaxy S7, then you will probably also use the energy saving mode, which is standard on board. Now it can be that you receive no more WhatsApp messages, if the Samsung Galaxy S7 is in standby.
This can be caused by the energy saving mode of the Samsung Galaxy S7. Because there is the option "Restrict all background data". If this option is enabled, various apps that require access to Wi-Fi or your mobile data connection are no longer working properly. This includes WhatsApp.
So if you notice that your WhatsApp messages are no longer up to date on the Samsung Galaxy S7, please check if the above function is disabled. To do this, open the following submenu on the smartphone:
Homescreen --> App Menu --> Settings --> Battery --> Energy Saving Mode
Now deactivate the "Restrict all background data" option by setting the controller to "inactive". Your Samsung Galaxy S7 should then again receive as usual all WhatsApp messages, even if your smartphone is not actively used.