An ongoing issue with the iCloud server is believed to have been fixed by Apple. The bug has persisted since November, and app developers were becoming increasingly upset with Apple's lack of effort to address the problem.
According to Hansmeyer, Apple said that it had addressed the issue that was causing sync failures.
Regarding the recent iCloud sync issue, I received a very kind and detailed response from Apple indicating that the underlying issue causing the 503 errors/sync failures has been fixed! 🎉 (Please share!)— Becky Hansmeyer (@bhansmeyer) January 26, 2022
Multiple developers have confirmed that the error messages appear to have gone away over the course of the issue.
The developer of the Tweetbot said that he has received reports about the iCloud over the past few days.
The number of iCloud Sync is broken reports we’ve gotten over the last 2 days has gone down to basically 0.— Paul Haddad (@tapbot_paul) January 26, 2022
I’d be interested to hear whether any devs/users have seen changes in iCloud sync reliability since this story broke. A couple of devs have told me they’ve already seen 503 error numbers dropping. Here, Cloud Battery is now working again, as is Transloader. https://t.co/JM57wqDp70— Craig Grannell (@CraigGrannell) January 26, 2022
It was a big problem for developers when the iCloud sync bug was introduced in late November or early December. App users experiencing iCloud sync issues don't know that it's a problem on Apple's end, causing developers to be blamed. Some app developers went as far as building a status dashboard into their apps to give end users a better idea of when issues were occurring.
Most developers say that the sync issue has been largely solved, but there are still a few complaints.
The sync issue is an ongoing problem that developers have been dealing with for months, and it is unrelated to the current two-day iCloud outage.