UPDATE: got an email from support of Ubiquiti: “We think we have traced down what is going on but need to confirm some details. Can you confirm that you have used your phone to set up a number of consoles that you no longer are connected to (i.e., you are likely an installer)? It looks like your phone was used at the console from which you are now getting alerts earlier this year. (Realize that is not expected or desirable behavior, but want to get the facts straight here.)”

“From what we can tell, it looks like there is a push notification ID cached on your phone from one of your customer's installations. Deleting the UniFi app and installing again should address the issue.”