When your Apple Watch stops receiving notifications, it's usually because it's lost its connection with your iPhone. When the two devices disconnect, your notifications don't bop over to your Apple Watch from the iPhone.
Check the connection remains by looking on your Apple Watch for a red iPhone icon or a red X icon. If either is present, it means the connection has been lost and you may need to move the devices closer to each other or repair your Apple Watch.
If Do Not Disturb is active on your Apple Watch, you’ll also not receive notifications. Learn how to use Do Not Disturb to avoid this at inconvenient times.