Messages do not arrive until entering the app (WhatsApp and Instagram)

Goodnight,

Something strange is happening to a friend with her iphone. For a month she has not received message notifications on Instagram, and the same thing has happened for two weeks on WhatsApp.

She does not receive notifications, she does not see red "balloons" or what is the name of the red icon on the app that indicates the number of notifications or unread messages.

We realized that indeed, WhatsApp messages do not receive them until they enter the application (so the problem are not in the notifications). We observe this since in this last time, whenever I send her a message, only one check appears (a single gray tick).

She made sure that both the iphone and the apps are updated to their latest version. We also check carefully that their configuration and mine (I have never had a problem like this) were exactly the same, both within the apps and the configuration of the iphone.

Something strange that happened to her today was that, for the first time the phone made a sound when sending her a message by wpp, and for the first time in these two weeks, the double check (two gray ticks) appeared when I sent the message. However, the phone did not emit the sound of the notification as such, it only produced a strange and brief sound; as if trying to reproduce the sound of the notification but they are to carry out this action. This only happened to her this time and with a single message.

She claims not to have installed any strange application, task killer or to have changed the phone or app settings.

Sorry for the length of the message, but I wanted to provide as much information as i can, so you can help me.

From already thank you very much for your time!