I am using pushwoosh to send notification from server to devices. And that is working without any problems. Also it is worth mentioning that I am using phonegap/cordova. This problem is only related for android, ios does not has this problem.
Problem is when I send few notifications in short time only one is displayed in android notification area. On notification handle in my code all notification are received. Notifications do not have same title or text.
You need to enable multi-notifications for Android. Look for "setMultiNotificationsMode" here:
https://github.com/Pushwoosh/pushwoosh-android-sdk/blob/master/Documentation/PushManager.md#setmultinotificationmode