Android notifications not coming?

Question

Android

The situation is the following. At one point, notifications stopped coming from everything on the phone: VK, WhatsApp, Instagram, mail.
I get them only when I go to the corresponding application. Those. as soon as I launch, for example, whatsapp, then all the messages that they wrote to me are immediately displayed (and so with all applications).
Work in the background, battery settings, everything is everywhere so that the applications do not turn off and work.
After I use the application, it works in the background for a while, i.e. all messages come, even though the phone is blocked, though not, but after a certain period of time, they stop coming again.
No updates have come to the phone lately, I haven’t installed new applications either (as far as I remember). I do not know where to dig to solve this issue.
Phone Honor 10, EMUI 9.1.0, Android 9

Answer 1

I have this behavior when battery saver is enabled