What does the red exclamation point mean in my scan history?

Using Avast Free Antivirus in Windows 10 PC (shows up on full scans but not boot scans)
Seems weird because there were no threats found…

It could be a notification (like you see in the avast tray icon), something not a virus as such. You could check your notification area and see if there is anything there

I have one, but no actual detections.