Looks like that with one of my systems (but it is only one system where I check situation yet) after three potential 'visible' system changes like:
-> installed recent monthly Windows Update;
-> installed CCF 3.15.225;
-> installed Antivirus 17.215.129;
with restart system after each event.
Start be next potential trouble:
>>> Received toast from FS Protection (for example, soon time limits; scheduled scan is start; detected malicious item is blocked) and it is visible.
>>> Toast is not read (system is idle, for example).
>>> System (Windows 10) with visible count of missed notifications (Notification area logo). For example, three items or one item.
>>> Choose such place to look what is it (which one toast/event) -> and there is empty screen (no fresh notifications).
Does it only my local experience or some of noted changes are valid for all (as reason for such situation with inability to look for 'missed' toasts)?
// later edited: sounds that situation (from spoiler) is pinned to something with my system. because situation is valid for system toasts too. Sorry for reply.
// one more update: later I found that there was activated (ON) Windows Defender with FS Protection at one time. Because I received a toast about Windows Defender own Protected Folders feature (which was introduced with recent system update and was ON as default) during opening scan log report by FS Protection. I decided to look for Windows 10 Security Center and found that Windows Defender is enabled/activated with all features. I decided to restart system else one time -> and all previous toasts are back to notification area (and was visible with limitation of twenty ones for each day/process). Both system and FS Protection 'missed/unread' toasts.
There seems to be serious memory leak. See my