notifications use firebase which is a google service, more on that here: https://companion.home-assistant.io/docs/notifications/notification-details
with that said we have heard of it being blocked before but thats more on a country basis, here I am just saying what can be the reason. If it works on your network then that might be a different ISP, mobile provider is a possibility because the notification makes no distinction between being home or not. It goes to one location and gets sent to you from that same location everytime.
maybe try clearing data in the app and log back in to see if that corrects it?