Samsung’s battery optimization settings often prevent certain apps from running in the background or receiving push notifications. It’s possible that this battery optimization is blocking your app from receiving push notifications.
Here are some steps to potentially resolve the issue:
Settings > Apps
.Battery > Optimize battery usage
.Settings > Device care > Battery
.App power management
.Apps that won't be put to sleep
.Settings > Notifications
.Settings > Apps
.Battery > App launch
.Manage automatically
is turned off.