Push Notifications for Self-Hosted on Discourse Hub?

Is this true for Android users? I have a self hosted setup, and my users who use android are saying they get no push notifications through the discourse hub app. If they use the PWA trick with a shortcut from their browser to their homescreen, they only get push notifications if they had opened it in the last 15 minutes or so.

Is this potentially a server configuration issue or reverse proxy issue cutting connections after X time?