Start by clearing your browser cache and cookies, including 3rd party cookies and restart your browser.
If that resolves it you should be good to go.
If it doesn’t try running your browser with add-ons disabled.
If that resolves it, have you added or updated any add-ons ?
If so try disabling that add-on - and restart and try again.
You don’t say what browser you are using:
If still not resolved and you are using Chrome based browser - try this suggestion by Avast Team member ‘lukor’
What about page notifications? Here: chrome://settings/content/notifications ? Do you have all cleared?