MacOS 27.2: Issue with symbolic links on SMB shares and FCPX?

Same problem here, and I can add some findings after a week of isolating it.

Setup: MacBook Pro (Apple Silicon), macOS 27.2, Final Cut Pro 12.4, Synology DS2422+ (DSM 7, SMB Service 4.15.13, Btrfs), 10GbE. Libraries on one share, media on another, imported with “Leave files in place”. Worked for years until the 27.2 update.

What I found inside the library: in Library.fcpbundle/<Event>/Original Media/ every clip is a 1067-byte file beginning with “XSym”. That is the format macOS uses to store symbolic links on SMB volumes that don’t expose real symlinks. A library from April on the same share has 159 of them and worked fine until last week. On 27.2 Final Cut still writes them when you relink, but the SMB client no longer presents them as links: Finder shows plain 1 KB files, and Final Cut tries to open a 1 KB “mp4”. First “Missing plug-in”, then “Modified file”, and relinking is undone within a minute.

What I ruled out: it is not the NAS. I set the SMB settings identical to a second Synology that I had not touched; that one fails the same way, with a new library and with an old one from a snapshot. Rebooting, NFS, nsmb.conf tweaks, Full Disk Access for Final Cut: no change. QuickTime plays the same files from the share without issues.

What works:

• Library on a local drive, media left on the NAS. Important: after moving the library you must do File › Relink Files › All and point it at the media folder on the NAS once. Moving the bundle alone keeps the broken 1 KB files, which may be why it didn’t work for you.
• Media copied into the library (no links), even with the library on the NAS.
• Others report that going back to 27.1 / 27.0.1 resolves it.

Same reports on r/finalcutpro with QNAP and another Synology. Filed with Apple via Feedback Assistant.

This macOS 27.2 issue affecting symbolic link behavior on SMB volumes has been reported elsewhere online. macOS 27.2 reportedly breaks the "Leave Files in Place" mechanism when the Final Cut Pro library itself resides on the NAS.

Under macOS 27.2, Final Cut Pro's internally generated symlinks—used to track external media—are interpreted as generic 1KB modified files instead of valid shortcuts, causing FCP 12.4 to lose track of the asset streams during playback.

Because your tests confirm that a local library referencing NAS media works perfectly, you can reportedly bypass this bug immediately without waiting for Apple's patch. 

Immediate Actionable Workarounds

Move only your .fcpbundle library package to your Mac Studio's local SSD while leaving all source footage exactly where it is on the NAS.

• Why it works: This completely sidesteps the macOS 27.2 SMB symlink bug. The local macOS file system handles the tracking links to the external NAS assets flawlessly.
• Setup: In FCP, select your library, open the Library Properties inspector, click Modify Settings, and ensure the media location is explicitly pointed to your external NAS folder. You can keep your cache local to speed up timelines

Full disclosure, I am passing this along but cannot test personally. I do have an NAS accessed via SMB, and video media stored on the NAS plays fine on my Mac running 27.2, but I do not use FCP.

Bugs should be reported to Apple here:

Feedback - macOS - Apple

FYI, second thread on this today. Here is the first.

macOS 27.2 – External media becomes unrea… - Apple Community