Hey all,
I've submitted a couple Feedback reports on this (FB22887867 on iOS 26 and FB24483266 on iOS 27), but wanted to share here for 1. validation that I'm not the only one experiencing this issue and 2. ask for ideas or experience with potential workarounds.
The issue is that AlarmKit alarms, even when properly configured and scheduled from an app, will intermittently fire late, or not fire at all until the iPhone is woken up.
For example, you might create an AlarmKit alarm with a relative schedule for 6:00am, then lock your iPhone before bed. When 6:00am passes, nothing happens. Then, at 6:13am it fires (with the full screen alert, audio and haptics)
Or, you might wake up at 6:53am, notice that it didn't fire, tap the screen on your iPhone, the Lock Screen displays for about a second, then all of a sudden, the AlarmKit alert presents (with the full screen alert, audio and haptics).
The issue has been present from iOS 26.0 up through the iOS 27.0 RC. I'm fairly confident that this is not a configuration issue. I've reproduced it using the WWDC 25 AlarmKit sample code and if you read from AlarmManager.shared.alarms, these alarms show up as expected: with a scheduled state and the correct times.
The issue seems to be more common overnight, when the iPhone has been asleep for a while. It's less common on my personal iPhone but occurs probably once out of every 3 to 5 alarms on my test iPhones (which have much less interaction and background activity etc.). Of our app's few thousand daily users, we get complaints at least once a day.
I've dropped a few sysdiagnose reports into Claude. In every instance, it claims that when the alarm was scheduled, mobiletimerd successfully registered an XPC wake-up for the alarm. However, during a completely unrelated event overnight (ex: a wifi packet), launchd drops the scheduled wake-up and nothing re-schedules it. So when 6:00am rolls around, nothing wakes up the iPhone to let the alarm fire. On days when it fires late, it's simply because another unrelated event (ex: a wifi packet) woke up the iPhone while the late alarm was queued.
Looking forward to hearing your thoughts.
Thank you.
