When the application is loaded or the user presses the sync button the latest weather information from the added locations is fetched from the server. Once this is done the new locations are merged with the old locations to manage the local subscriptions accordingly.
The issue here is that sometimes locations from the server are not in the same order of those on the client. This could result in locations and subscriptions not matching after syncing them with the latest data.
If you tap a location to add notifications and choose to block notifications, subsequent taps on the notification icon should detect this and let the user know they need to manually reenable them.