Loose notifications

Hi, I'm having a real issue with notifications on my android phone, once set up, the doorbell works fine, get notifications, can be slow to come through, but once I have left my house and switched from home network to mobile connection, after about an hour or two I don't get any notifications at all, even when I return home ang get back on my home network, I need to disable and restart notifications in the app, but it will do the same next time I leave the house, I have reinstalled the app 5 or 6 times and also done full factory reset on my phone, I do get notifications in the first hour or so when I leave home, so now I'm at a loss as what to do? Any ideas?