I was having the same problem ... Chrome ... found the following and it worked for me:
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@User17296935248812240630(Customer)
8 months ago
In your browser go to ..
edge://settings/content/cookies/siteData?searchSubpage=lastpass
.. or ..
chrome://settings/content/all?searchSubpage=lastpass&search=cookies
.. and delete each individual cookie.
Now go back to lastpass, hit CTRL+F5 and your notification box should be gone.