The Action Center is reportedly broken for some users in Windows 10 October 2018 Update. According to reports, the Action Center doesn’t show notifications in Windows 10 after installing the October 2018 Update (version 1809).
A thread on Reddit documents a bug where the Action Center in Windows 10 October 2018 Update fails to display the notifications. There is another thread on Reddit which confirms this problem.
A Microsoft employee on Reddit also confirmed that there is a bug where the Action Center would appear on the left side of the screen instead of right on some systems.
It turns out that Microsoft has already figured out a fix as the latest Windows 10 Build 18267 (19H1) for Insiders has addressed the reported issues. It’s likely that Microsoft will backport the changes to Windows 10 October 2018 Update and address the reported issues with the November cumulative update.
In the changelog of Windows 10 Preview Build 18267, Microsoft confirmed a bug where the Action Center might appear on the opposite side of the screen before appearing on the correct side. The company also acknowledged an issue where the Action Center is blank but the icon shows unread notifications.