On Windows 10, Action Center is a feature that groups app and system notifications and puts them into a single interface that can easily be accessed using the taskbar. In addition, Action Center also hosts the quick actions buttons to help you get access to your most-used settings and apps quickly.
Unfortunately, several users have been reporting that after upgrading to the Windows 10 October 2018 Update (version 1809), notifications no longer show in Action Center. While it may seems just another bug in the pile of problems with this feature update, this issue can be traced to the background app feature.
How to fix Action Center notifications with Windows 10 October 2018 Update
To start seeing notifications again in Action Center after upgrading to the October 2018 Update, use these steps:
Click on Privacy.
Click on Background apps.
Turn on the Let apps run in the background toggle switch.
If the option is already enabled, on step No. 4, turn off the toggle switch, restart your device, and then turn it on again.