Hi, this is most probably caused by some specific settings of your network (perhaps your router has some security system of its own).
To disable the notifications please follow these instructions:
- open the Avast Mobile Security app
- tap the “three-lines icon” in the upper left corner of the screen to bring the menu
- in the menu select “Settings”
- tap on “Notifications”
- right there turn the “Potential Wi-Fi issues” off