Notification in backend doesn’t disappear

Hi, Your plugin is very useful but I have a problem….
This notice:

WC Price History
WC Price History plugin is scanning products to set their initial price history.
While this process is going on, please refrain from editing products.
We will notify you when the scan is finished.

..doesn’t disappear from my backend. It’s now more than a month that I’ve installed the plugin and the notice remains. But the plugin works as expected with no problems in frontend.
How can I make the notification disappear? I had tried uninstalling and reinstalling the plugin before, but nothing changed.

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