macOS Tahoe 26.4 brings several new features to Macs. But it also breaks one critical functionality: Time Machine backups.
The bug appears to affect backups over network drives and NAS (network-attached storage), causing them to fail with a credential error.
Time to create a backup strategy for your backups
Time Machine is a great way to create a thorough backup of your Mac. Many power users prefer backing up their Mac to a NAS, like the Ugreen DH4300 Plus. This removes the hassle of connecting an external hard disk to the Mac for creating a backup.
However, with macOS 26.4 Tahoe, Apple appears to have broken Time Machine backups over the network. There are hundreds of reports from frustrated users on Apple’s support forums, complaining about Time Machine backups failing to initialize due to repeated credential errors. Apparently, the bug first appeared in macOS 26.4 beta 2, but Apple never got around to fixing it.
The issue also does not appear to be limited to a specific NAS. It persists across all NAS, including those from Synology, Ugreen and TerraMaster. It also doesn’t seem tied to invalid credentials, as affected users can still mount their NAS on a Mac without any issues.
A complicated workaround exists
One potential workaround involves manually updating the serverMarkers.plist file with your NAS backup location. Specifically, if your system logs show errors like NAConnectToServerSync failed with error: 80, adding your NAS hostname to the plist file may help restore backup functionality. You can find more instructions on this Reddit thread.
However, this is an advanced fix that requires using Terminal with root access, so it may not be suitable for all users.
Alternatively, there are reports that Apple has resolved the issue in the first macOS Tahoe 26.5 developer beta. So, if you don’t want to manually make changes to the Plist, install the latest Tahoe beta. Or, wait for its public release, which should happen sometime in late April.
Rajesh has been writing about consumer technology for over a decade, with a strong focus on iPhones, Macs and Apple’s ecosystem. He enjoys digging into Apple software updates, hardware changes, and discovering new Mac apps that make work faster and more enjoyable.
