iPnone doesn't notify about messages with display turned off

Hello! Problem appeared recently. iPnone 7 (almost new) doesn't display 1/2 of notifications about arrived messages when display turned off. Half of them arrive alright - ping and some vibe and display turns on and notification - and half arrive without ANY singnes at all. No beep, no vibe, no display turning on - nothing! Yet when i take iPhone I see them on the diplay.

Can anyone tell me what can be the problem? I really doubt thats a hardware problem.

Any other notifications (foe example, sleep reminder) are not displayed corrrectly also.

Message was edited by: Alejandro_64