I'm not sure if I've found a bug or not but thought I would report it to you.
I had defined a water leak sensors under the 'water' section of HSM.
I have since deleted them but when one goes active it shows as an 'Alert' in red against the app.
As you can see nothing is defined.
Under event subscriptions it shows the devices that were there previously.
If I open up HSM and select done the red alert notification goes.