iOS 26.4 CloudKit Bug Disrupts iCloud Sync, Fix Coming

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Originally published at: iOS 26.4 CloudKit Bug Disrupts iCloud Sync, Fix Coming - TidBITS

It’s always hard to know how long to recommend waiting before installing new operating system updates. In “OS 26.4 Adds AI-Generated Playlist Playground, Separates Family Sharing Purchases,” 25 March 2026, I chose a relatively short time, saying, “If you have already made the leap to OS 26.3, I recommend waiting a few days to make sure no surprise bugs crop up, then updating all your devices.”

Unfortunately, in the case of iOS 26.4, that may have been optimistic. If you’ve noticed that apps relying on iCloud sync have stopped updating in real-time on your iPhone or iPad since updating to iOS 26.4, you’re not alone. A bug in iOS 26.4 has broken CloudKit push notifications—the mechanism that tells apps when new data is available in iCloud.

While your devices can still send changes to iCloud, apps on devices running iOS 26.4 (or likely iPadOS 26.4) may not receive the silent notification that triggers a sync. The developer who originally reported the problem said leaving and returning to the app allowed the sync to proceed, so if you’re seeing syncing problems, switch to another app and back. Macs, Apple Watches, and Apple TVs seem to be unaffected.

The bug may not affect every device—one developer reported that a tester running iOS 26.4 didn’t experience it. Nor does it prevent every iCloud-savvy app from syncing, since apps often have fallback mechanisms in case push notifications fail. That’s the case with Drafts, whose developers are reporting slower sync times. Importantly, data isn’t lost; it’s just the real-time push notification that fails, so syncing will still occur when you relaunch an app or switch away and back.

Although nearly 20 developers confirmed experiencing the bug firsthand, and one noted that even Apple’s Passwords app appears to be affected when syncing shared passwords, I was unable to reproduce the problem in Passwords or several other iCloud-savvy apps. The closest I could come was in Agenda, where a change made on one Mac synced to another Mac significantly more quickly than to my iPhone running iOS 26.4.

The good news is that Apple has acknowledged and addressed the bug, and multiple developers have confirmed the fix is present in the iOS 26.5 beta. However, that release may not appear until mid-May, so we can hope Apple will release an iOS 26.4.1 patch to address it sooner. If you’re still using iOS 26.3 or iPadOS 26.3 and rely on quick iCloud syncing, consider holding off until the next update.

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I wonder if the bug impacts the new Apple Business services, especially email, calendar, and directory services. If so, it’s really quite an embarrassing bug, both for Apple and for Apple advocates within businesses.

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Thanks for the update. I was about to update my desktop Mac from macOS 15 to 26, in order to align with my new laptop (which shipped with 26 preloaded). But seeing this, I’ll wait for one more update (26.4.1 or 26.5) and stay on 15.7.5 for a bit longer.

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Just a note that MacOS is fine - it’s iOS and iPadOS that are having issues. So you should be all set on the desktop Mac.

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The various aspects of what folks consider “iCloud” is actually surprisingly varied.
In a most timely fashion, Howard Oakley has just written a great little explainer as to which parts of iCloud exist and which parts depend on what other parts (if any).

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This is probably not the same thing, but I noticed that my iPhone Health app stopped updating my “sleep score” (including all sleep data) as of April 1 (Fool’s day?), yet I haven’t updated my watch (26.3) or my primary Mac (26.3.1) or my iPhone (26.3.1(a)). I did update my iPad to 26.4, but I don’t use it for much besides Angry Birds Unloaded. I did update to 26.4 a secondary iMac (2024) that I’m preparing for a business use. I figured it was maybe an April Fool’s joke or simply that I hadn’t restarted my iPhone or my watch in ages. I turned off both and restarted them yesterday (Sunday), and today everything is copacetic again. But it’s probably just a coincidence unrelated to the CloudKit push issue. Despite this being the first time it’s failed to sync since whatever introduced “sleep score.” Unless updating two devices (the iPad and the repurposed iMac) triggered the problem for Macs and devices still in 26.3x.

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I tried creating a note (iPhone iOS Notes) and it showed up on my Mac Notes version. Also, I sync my 1Password with my iCloud drive and its updating so I wonder if its specific apps?

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Notes are actually implemented via e-mail messages (I assume via IMAP interactions).

For example, I’ve enabled Notes for my GMail account. If I create a note on that account, I see it in GMail as a messages with a “Notes” label. If I delete that message from GMail, it vanishes from the Notes app soon afterward.

I don’t know for sure that this is how Apple is syncing Notes saved to iCloud accounts, but I think it’s a logical assumption that it is doing the same thing for all Internet accounts.

So, I would expect Notes syncing to keep working as long as the IMAP protocol (underlying Mail as well as Notes) is working.

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If Notes was affected, this bug would be seen doing it the other way - updating a note on the Mac and then seeing, if you have the Notes app open on the iPhone, whether it would be updated.

I’m not sure if Notes is affected.

The other thing about this bug is that often closing the offending app on the iPhone or iPad and then activating again makes the updates happen.

What’s been frustrating for developers, I think, is that their apps are not getting push notifications while they are in the background so when a user opens the app, they find the data is incomplete.

I’ve seen a story in 9to5mac that 26.4.1 may be imminent, but the story did not mention this issue at all. (It didn’t mention any specific bugs, just that 26.4.1 was being registered as being installed in the wild and connecting to 9to5mac’s website, presumably by Apple’s testers.)

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iCal did not update across devices and I was scheduled for several events at the same time. Looking forward to the fix!

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This is why I wait until August to make sure all the bugs have been worked out.

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I had this with Notes. Updated 2 notes on my Mac, but it wasn’t showing up on my phone for over a day. All working OK now.

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I’ve definitely noticed a lag in updates. I’m not 100% sure if it’s related, but I’ve definitely noticed a delay in updates, especially from the Sports app. Scores from games don’t update on my iPhone’s lock screen anymore.

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