In recent months (or year) the macOS app on Mojave 10.4.6 (MacBook Pro) and current Catalina (MacPro) more often than not will sound the wind-chime alert but when app opens there is no event. This event is viewable on iOS iPhone or iPad when I check. The event eventually appears on macOS.
Sometimes the event appears and video window opens just the way it should. I have not figured out why it works sometimes but not most of the time. Doesn’t seem to matter if the app is open at the time.
Possibly related: When events occur when the Macs are asleep, wind-chime alerts often sound immediately when the Mac awakes. Doesn’t bother to open video window but I can check the history to see video.