Background mode not working anymore in iOS

Everything is working fine when the app is on. However, when I kill the app, the notification does not popup. I set the location service to be ‘always’. Bluetooth is on. It seems to me that there is something else that I need to enable. What would that be in iPhone settings? It used to work until last week. I am not sure what I changed.

It just started working after a few hours. I am using iOS 12.4. So, should I assume that background mode is not reliable? I am not sure if the cause is the app or iOS. FYI - I am running two apps. One that I made based on the notification template. The other one is just a notification template. They both stopped working for background mode and just started working again at the same time.