Users may notice the following scenario:
Upon login, criteria for a banner to appear is met, and the banner is displayed to the user. The user clicks the 'x' to dismiss this message. They then log out, and log back in, and as expected, the banner no longer displays (because they have already dismissed it.
Later, the user clears their browser cache/cookies, or uses incognito mode, or another browser entirely. Now upon login, the banner reappears despite already have been dismissed previously.
This is expected behavior. Many/most banner notifications have their dismissal response stored in browser cache. Therefore, clearing this cache will remove the dismissal response and the banner will display again despite being exited previously.
One example of a banner with this behavior (this is not an exhaustive list) is the optimal speaker separation banner, which has the message, "Your Salesforce admin has turned on optimal speaker separation. You can make changes in your personal settings."
Other examples of banners that store dismissal state in browser cache include: the 'Get Started' setup assistant banner, the 'Try the new Salesforce mobile app' banner, and feature announcement banners displayed at login.
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