Why don't I receive notifications from online apps?

[AC Question]

While using a rooted Huawei y300-0100 phone, I don't receive notifications from online apps. For example, if someone sends me a message on facebook, the facebook messenger app won't notify me for a period of time, I get the notification pop-ups after 40 minutes if i am lucky (it otherwise takes some hours), or if I manually refresh the app. It's the same with other apps like whatsapp, snapchat etc. This problem takes place whether I am connected to a wi-fi or to data connection.
Does anyone know what the problem is and how can I fix it?
Thank you in advance for your help.