macOS 27 Beta 3 with fatal file system error? | News

At the beginning of June, Apple showed iOS 27, iPadOS 27 and macOS 27 to the world for the first time at the Worldwide Developers Conference 2026. Apple focused heavily on fixing bugs and annoyances with these releases – and even showed insight into Liquid Glass and rolled back many unpopular changes. If you look around forums and social media, the new operating systems have been received positively so far.

Apple has not yet released a public test version of macOS in the Public Beta Program – the current version is only available to registered developers. This circumstance could be a stroke of luck, as there are currently some reports doing the rounds that the third pre-release version of macOS 27 may have a serious bug.

APFS file system breaks
There are various reports circulating that some time after installing the third developer beta, the APFS file system usually has uncorrectable errors. For most of those affected, this seems to manifest itself in the way that the Mac becomes significantly slower during use, apps no longer start or certain folders or files can no longer be opened.

If you then examine the hard drive with the disk utility, the check either freezes or numerous errors such as “invalid o_oid”, “invalid o_xid”, “fsroot tree is invalid” or “unexpected security xattr” are found.

Time Machine as a reason? Destroyed backup?
A striking number of those affected report that Apple’s backup solution “Time Machine” is activated on exactly these Macs. Time Machine uses snapshots of the APFS file system to create consistent backups. A serious error may have crept into macOS 27 Beta 3, which leads to the corrupt file system.

According to some reports, the error in the file system could also be transferred to the backup, because for some users the backup volume also has uncorrectable errors – and the backup is unusable.

A lot is still unclear
However, the exact circumstances that lead to these problems have not yet been clarified and the reports do not yet provide a completely meaningful picture. Not all users are affected by the problem – but to be on the safe side, you should avoid installing the third beta of macOS 27 until more information is available.

Never in the productive system
Developer previews are intended for programmers to test their own apps early and provide feedback to Apple. Such problems, as described above, have rarely occurred in the past, but cannot be ruled out with such early test versions. For this reason, you should only install early pre-release versions on devices that do not store important data and on which you are not dependent.