You might have Do Not Disturb enabled which is a feature that blocks all notifications. It can activate automatically, usually during late evenings and disables itself in the morning.
Do Not Disturb Switch
1) Click the most top right icon in the menu bar to bring up notification center.
2) Scroll upwards. This will reveal the Do Not Disturb switch. Disable Do Not Disturb. This change is only temporary – for permanent settings scroll down further.
Do Not Disturb Settings
To permanently change your Do Not Disturb settings, head to System Preferences > Notifications:
And just to be sure, check your settings in System Preferences > Notifications > Gestimer:← Why am I not receiving any notifications?