Notifications count seems to not be working properly sometimes

Steps to reproduce:

1. Log in as Admin
2. Install the Blog app
3. Create a new user
4. Log in as that user and set the Notifications to ON for Blog and Pages, for both Notification menu and Email
5. Log in as Admin
6. Create new blog posts and publish them
7. Create new pages, edit them, comment, add attachments, delete them (at least 10 actions for the notifications events)
8. Log in as the simple user and notice the Notifications list
9. Log in as Admin again
10. Create new blog posts (published), pages, edit them, comment, add attachments, delete
11. Log in as the simple user
12. Observe the number shown on the bell and the number of events in the Notification list

Expected results: The count of events match with the number of events shown in the list.

Actual results: The count appears to be lower then the numbers of events shown in the list. I can't seem to find a pastern on why this is happening. The first time I see the notifications as the simple user I get the right count but as I log back with admin and create more events the count seem to be not working properly anymore in my list there are 26 entries and the count appears to be 19. See https://up1.xwikisas.com/#u_PFBHf36fUxorz09BwKDQ

I've also tested this with Chrome 67 and Firefox 60 - I get the same result. The issue is I can't reproduce a pattern. The count seems to be randomly working/not working. I've cleared all cookies but same result.