Push Notification Issues
Delivery of notifications depends on lot of factors. Here we tried to list all possibilities and ways to fix it.
Notifications are highly reliable, except when device manufacturers interfere. In an attempt to increase battery life many device manufacturers have modified the Android operating system in ways that interfere with prompt notification delivery. Please check the article in the given link to see if your device is listed and follow the fix as per your device.
Link to article: https://onesignal.com/blog/manufacturers-interfere-with-reliable-notifications/
On iOS
