I was updating the core, which for some reason takes forever in 95% (on a fast machine on an M.2 based VM).
I instinctively pressed F5 after some time, the notification was no more.
I expect the system to re-pop the notification since it didn’t finish yet (probably).
I don’t think I just pressed F5 at the right second.
You can probably verify by making the system go on a long process with some progress and see if you can still see the notification after page refresh.
It is possible it does refresh if the percentage changes, but it seems actual progress of some tasks isn’t also the strong card of NS8 (not that I know of any OS doing a good job).