@Atomatth I took the liberty to put this together. Hope it helps peeps.
Plex Media Marked “Unavailable” on Mac (Synology NAS via SMB) – Root Causes & Solutions
Understanding the Issue and Symptoms
Many Mac-based Plex Media Server users (especially on macOS 15 “Sequoia”) have reported a strange issue: Plex suddenly flags a large portion of their library as missing (red trash-can “unavailable” icons) even though the files still exist on an external NAS. In these cases, Plex may stop updating new files and mark existing ones as “unavailable,” yet local playback (or third-party players) can still access the files. Remote Plex clients, however, fail to recognize/play those items because Plex believes the files are gone.
This often occurs sporadically and without a clear pattern. Sometimes after a manual or scheduled library scan, you’ll see perhaps half your TV shows or movies suddenly marked with the trash icon. If Plex’s Empty Trash feature runs at that moment (either automatically or manually), it can purge those entries from your library—causing you to lose posters, watch history, and metadata until the files are re-added later.
IMPORTANT TIP: Disable “Empty trash automatically after every scan” immediately to prevent data loss while troubleshooting.
Users have observed that this bug tends to affect network-mounted media (e.g. SMB shares from a NAS) on macOS 15+. One person described it as a “yo-yo” – a scan might randomly mark a set of files unavailable even though they’re present, and a subsequent scan might bring some back while marking others missing. In one case, two-thirds of an entire library was erroneously deleted from Plex after a scan, despite the files still residing on the NAS.
Importantly, this mostly seems to happen on macOS, and started after upgrading to macOS 15 “Sequoia” – strongly hinting that something changed in Apple’s network filesystems.
The issue doesn’t appear to be caused by Plex settings or network dropouts (the NAS and network are otherwise stable), nor by user error; rather, it’s a compatibility bug between Plex and the way macOS handles SMB-mounted drives in recent versions.
Root Cause Analysis: macOS SMB Bug
All evidence points to a bug in macOS’s SMB client introduced around macOS 15. In short, Apple’s SMB network-drive handling is not reliably reporting directory contents or connectivity status to Plex.
Plex relies on the OS to access the files; if the OS intermittently fails to see the files or times out, Plex will think those files vanished. Community experts and Plex staff confirm that this problem is due to a buggy SMB implementation in recent macOS versions. It’s not purely a Plex bug—other software that heavily accesses SMB shares can encounter similar issues—but Plex’s library scanning makes the problem very visible. In essence, the Mac is losing the mount or cache briefly, or returning incomplete directory listings, and Plex interprets that as files being gone.
Specific Technical Factors Theorized
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SMB Directory Caching/Leasing Issues
macOS 15 introduced changes to SMB caching. When a folder contains a very large number of items (e.g. > 1 000 files or subfolders), the Mac’s SMB client might not report all of them to Plex during a scan. This can make Plex “drop” media entries during library updates due to stale or limited directory caches. Disabling client-side directory caching on macOS completely stopped the disappearing-files problem for some users. -
SMB3 Multi-Channel and Protocol Quirks
Mac Minis with Apple Silicon and fast networks can use SMB3 features like multi-channel. There’s anecdotal evidence that SMB multi-channel or signing on macOS contributes to instability. Turning off SMB3 multi-channel support on the Mac (along with other tuning) greatly improved stability. Multi-channel is meant to improve throughput by using multiple connections, but if there’s a macOS bug in its handling, it could cause the share to reset or drop under load. -
Lack of Real-Time Change Notifications
Unlike local disks, network filesystems on macOS don’t send instant “file changed” events to Plex. Plex won’t know a file is gone or added until it scans or tries to access it. If the NAS drives are asleep or the connection has transient hiccups, the first access could fail. However, in these reports the NAS was accessible outside Plex and files could be manually browsed, so a simple timeout due to drive spin-up is likely not the primary culprit. It’s more about the OS erroneously reporting files as missing or not letting them all be seen as they need to be. -
macOS 15 Network Stack Changes
Early in macOS 15’s release there were known networking issues affecting VPNs and security tools. Some users suspect the macOS firewall or network stack might interfere with SMB traffic. Temporarily disabling the macOS firewall has been suggested as a test. While not a confirmed fix, it’s worth ensuring nothing in macOS is actively blocking or timing out your NAS connection.
Solutions and Workarounds
Several effective workarounds have emerged. You may need to combine these to fully solve the problem:
- Tweak macOS SMB Client Settings (
/etc/nsmb.conf)
Create or modify/etc/nsmb.confon your Mac with:
[default]
dir_cache_off = yes
mc_on = no
dir_cache_off = yesdisables client-side directory caching.mc_on = noturns off SMB3 multi-channel.- After creating the file and rebooting, Plex should no longer “lose” your media during scans.
-
Adjust Synology SMB Server Settings (Enable SMB3 Leasing)
In DSM 7.2+ under Control Panel → File Services → SMB → Advanced, enable SMB3 directory leasing for all shared folders. This improves client-side locking and helps macOS enumerate files reliably. -
Use a Persistent, Single Mount
Continue using AutoMounter (or similar) to keep the NAS share always mounted. Ensure macOS isn’t also mounting the same share via Login Items or Recent Servers, which can create duplicate mount points and confuse Plex. Aim for a single, never-sleeping mount point. -
Prevent Automatic Library Trash Removal
Disable Plex’s Empty trash automatically after every scan (under Settings → Library). This avoids turning a temporary glitch into permanent data loss. With auto-trash off, accidentally marked-missing items will return on the next scan once the share reconnects. -
Consider Alternative Protocols or Clients
- NFS: macOS supports NFS mounts and they tend to be very stable for continuous media streaming.
- AFP: Although deprecated, AFP can still be used on macOS and Synology. Some users found AFP mounts did not suffer the SMB-related “trash can” issues.
- Third-party SMB (e.g. rclone’s go-smb2): Bypasses Apple’s SMB stack entirely, avoiding the bug, though with slightly lower performance.
- Keep Systems Updated & Monitor for Native Fixes
You might want to apply macOS and Plex Media Server updates as they arrive. Up to you. Apple or Plex may eventually address the underlying SMB bug. If a future macOS release fixes it, you can remove the custom/etc/nsmb.conftweaks file.
Conclusion
The Plex “files unavailable” issue on Mac Mini is not user error but a macOS SMB client bug introduced in Sequoia. Plex reacts to what macOS reports—if Apple’s SMB implementation briefly fails, Plex flags media missing. A true fix likely has to come from Apple.
By disabling directory caching and multi-channel on the Mac, enabling SMB3 leasing on the Synology, maintaining a single persistent mount, and disabling auto-trash in Plex, you can work around Apple’s SMB quirks and keep your library intact.
Should the problem persist, fallback options include NFS, AFP, or third-party SMB clients. In the meantime, these workarounds will help ensure your Plex server remains connected to your Synology library without losing metadata. Good luck!
