First, be sure that your reminders are toggled ‘ON’. Alerts for individual tasks can be toggled ‘ON’ by tapping on the task to see the task options and then tapping on the bell icon to open the reminder settings. If they are toggled 'ON', please clear the app data from the device settings (Settings→Apps→Any.do→Clear data) Then, uninstall and re install the app.
Note that there is currently a bug with Leonovo Z2 Plus that prevents notifications from all apps from popping up. They are working on a fix for this issue.