Notification popups sometimes not clearing

I have Macrium Reflect notifications turned set to "Show notification banners" on and "Show notifications in notification center" off. Usually the popup (which is technically a "banner", I guess) clears in a few seconds. Today I noticed on hanging around. I manually closed it an discovered 7 or 8 other Reflect notification popups underneath (which I closed, one by one). Shortly thereafter another Reflect notification displayed but it cleared in a few seconds (as usual).

I get very few notifications other than from Reflect so I don't know if this was specific to Reflect or if no notifications would have automatically cleared.

I vaguely remember hearing that the time to clear notifications was not particularly reliable, but I don't remember ever hearing that they sometimes failed to clear. Does this sound familiar?

You can remove the Hourly Notifications from Macrium Notifications

Spunk said:

You can remove the Hourly Notifications from Macrium Notifications

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I think you misunderstood my comment/question. I'm not getting hourly notifications from Reflect (and didn't even know they existed). These are just the "Backup started" / "Backup ended" notifications, and I want those. I am asking what would cause these notification popups to not automatically clear after a few seconds. After the 4th or 5th backup of the day I noticed that a backup was still being displayed after many minutes, and when closing it I found a whole pile of other notification popups queued behind it.