heikwith said:
Thanks fir that.
I fast did some additional tests in the RTM 1809:

Reboot with disabled background apps.
Creating message in action center with a scan with Windows Defender
Got a 1 in the action icon in the tray.
Clicking on it gives an empty message screen.
So wrong.

I enabled background apps and did the test again.
No success.
Then I did a reboot (so with enabled background apps)
Test again and again a 1 in de tray.
I clicked on de tray icon and I got all de missing messages !!

--> So after enabling the background apps I need a reboot to get it into work

Then I disabled the background apps.
Test again.
Messages still OK !!

I rebooted with disabled background apps again.
Test again.
And now message screen again empty.
So wrong again.

I have no time to test this further now.
Bij the way, in the above test I enabled/disabled all the background apps.
Probably only one of background apps should be kept enabled to get a success.
Did you test that already ?
Reboot or restart of the shell experience host process