android notification missing if phone was temporarily offline or rebooted

I found two situations, when notification is lost on android devices:

• if message, which should cause notification is sent while phone is rebooting. After booting (app has autostart), notification for such message is not delivered. If other message is sent, for new one is notification displayed (but never for first message)
• if message, which should cause notification is sent while phone is not (temporarily) connected to internet. After reconnecting, notification for such message never arrives. Only notifications for newer ones.

It is making me little nervous, as i'm loosing important notifications.

Tried with other phone, different brand and same story. Both were android 10.