There are several reasons why WhatsApp can block the preview of received messages. Solving it is simpler than you think.
Multiple users of WhatsApp They reported that they do not receive a preview of the messages until they open the app. This is usually uncomfortable for those who expect an immediate response. In order to see them they have to open unlock the cell phone in case they have a password and open the app later to observe the message.
In that context the app gave a series of explanations about what happens.
One of them is that notifications for the entire application may be silenced. To do this, it is necessary to verify whether they are activated or not.
Another situation that may occur is the lack of connection or poor Internet on your phone. If you can enter the web pages, but WhatsApp It doesn't work, you have to contact your telephone company to check that you have access to your non-web connections and socket. The latter is the connection between the client and the network server).
It may also be activated the option to restrict data and you have not noticed. To solve this problem you must enter the application administrator from settings and check that the restriction “Network background data” is deactivated. The same should happen with Google Play Services.
Finally, if everything still remains unchanged, there are other possible solutions given by the application. One of them is to turn off your cell phone for 30 seconds and turn it on again. Then you have to connect the phone to a power source. Once plugged in, you must uninstall any task manager from your phone, check that the application has all permissions enabled, and so on.
WhatsApp: if you want to keep the quality of your photos do not share them by the app