In the app we are developing, we update the device token upon app launch using didRegisterForRemoteNotificationsWithDeviceToken. Previously, after an iOS major update, if the app was left without being launched, users experienced an issue where notifications would not be received. Later, we confirmed that running didRegisterForRemoteNotificationsWithDeviceToken during app launch updates the device token and restores the ability to receive notifications. Therefore, we believe that the device token may change due to an iOS major update. We want to understand the detailed conditions under which the device token is updated due to an iOS update: Does the same issue occur after iOS minor updates as well? Does it always happen during iOS major updates? We reviewed the official documentation, but there was no detailed description of the device token update conditions. Additionally, we contacted Apple, but received no clear answers. If anyone has experienced the same situation, we would appreciate any information you can share.

I am sending push notifications to the app with critical alerts, but there is a significant delay. If the number of target devices is 1000 or less, notifications will be received normally within a few seconds to a minute. Once the number of target devices exceeds 1000, some devices will arrive quickly (normally within a few seconds to 1 minute) and others will arrive late (3 minutes to 15 minutes, divided into hundreds of items). In severe cases, notifications to more than 80% of devices will be delayed. Example: If you send 3000 notifications at once, 　1 minute: Notify 400 items 　5 minutes: Notify 1000 items 　10 minutes: Notify 1000 items 　13 minutes: Notify 600 items *The timing of 5 minutes, 10 minutes, and 13 minutes changes every time and is not at regular intervals. We understand that according to the push notification specifications, sending several thousand messages at once is not a problem. Please let me know if there is a rule, such as sending 1000 items at a time, in order to deliver quickly and with minimal delay.