[AC-6665] Problems with push notifications (do not arrive or come multiple times)

We sent a push notification yesterday. According to the log, around 11,000 pushes were sent. Some Android devices were listed with the error code 3009. Now users who have received multiple push notifications have reported. In contrast, some (including iOS) have not received a push notification. Are there any explainable reasons for this? Are there still detailed logs? How can the list of registered devices be cleaned up meaningfully so that there are no duplicate entries? When an app is deleted and reinstalled, a new device entry is always saved, but these get the same push channels. Could it be that several push notifications are received as a result (especially with Android)? We must be able to explain the behavior to the customer and justify any necessary changes / adjustments. Many Thanks