Sequoia Time Machine Synology NAS keeps disconnecting

Bravo. I disabled MacOS Network Firewall and the backup immediately started running. Per some other posts with similar results, I will let it run a few days and then

1) re-enable firewall with current settings. if that fails again, I'll

2) re-enable firewall with updated settings to accommodate Time Machine settings.

Thanks much for the help

Update 29th Oct: After updating to macOS 15.1, I'm able to backup to my NAS with Time Machine without issues (with Lulu and firewall enabled).

What worked for me:

1. Update macOS to 15.1
2. Disable firewall
3. Update Synology DSM to the latest version - this for some reason I had to do manually for my DS218+. Use this tool to check if you have the latest version: https://www.synology.com/en-ph/support/download

Not sure which of these is an actual fix, but 1+2 definitely didn't help. Only when I did 3 it started backing up.

I encountered the same issue on a 2023 M3 Pro MacBook Pro, typically after computer waking up from sleep. My MBP is connected to the same subnet via both Wi-Fi and a Thunderbolt Ethernet dongle. The backup target is in another VLAN (there is an OPNsense FreeBSD firewall doing L3 routing in between). The TM target is discovered using mDNS (which is repeated by the firewall cross VLANs using mDNS repeater). The Synology is a DS220j running latest DSM.

When the problem occur, the Synology's Resource Manager shows two concurrent connection from my wired IP address to the TM share. I have to kill the older one for TM to work again. This is the workaround I used anytime TM stopped working because of this.

The problem started occurring after upgrading my MBP to 15.0 few weeks ago. I tried eliminating few other probabilities including 1) performance issue with the NAS; 2) L3 firewall state tracking with the pf on my OPNsense firewall when doing inter-VLAN routing and persist idle long connection; 3) concurrent Wi-Fi and wired connection. I come into conclusion that macOS is the most probable one to be blamed.

I have upgraded to 15.0.1 last night and it seems I did not encounter the issue again after waking up the computer this morning. Will continue monitoring the issue.

I was getting similar errors. When I log into the web interface of my diskstation, I can see that when I try to start a TimeMachine backup, it creates a new SMB3 connection to the diskstation. If I delete any previous ones, then the new connection can connect and access the backup and run successfully. If I have multiple SMB3 connections, then the backup fails. I can see connected users (and disconnect ones I don't want) via widgets.

I'm on MacBook Pro M1 with Mac OS X 15.0.1. With firewall turned on, all my Time Machine backup would fail. To the Synology NAS or to a USB drive. Tried adding Full Disk Access to the Time Machine app to Privacy & Security and it didn't help. Just had to turn it off for both to work…

I confirm my problem is fixed after upgrading to Sequoia 15.1.

After 15.1, I ran a backup with firewall off - worked fine, as it had since I turned off firewall with 15.01

Turned firewall back on, ran new backup - worked fine.

Now resolved.

This worked for me. My synology DS218+ hadn't updated past 7.1.1 because of an old package I had installed that was no longer supported in 7.2.2. Updated to the new version manually, and it started backing up immediately.

The update 15.1 (24B83) fixed the issue for me with my WDMycloud.

Apple is not to blame if the Synology Server does maintain a proper TM handshake. Synology doesn't use a licensed version of Apple software. They are forced to use a public domain version of AppleShare that may simply not yet be compatible with a new major release of macOS such as Sequoia. That puts Synology in a bind too.

There are things that one must handle in the Synology Diskstation configuration settings too such as keeping current with DSM 7.2.2 and ensuring that in Control Panel > File Services you are using SMB 3. Synology has this Mar 4, 2024 article on Time Machine though that may not be enough if there is an incompatibility lurking.

I have a new DS119J downstairs with DSM 7.2.2 and 16 TB configured and I still don't attempt TM backups to it. Otherwise, file sharing works just fine with released Sequoia v15.0.

I am afraid the problem is on Apple's side.

I have a Synology DS218+ at home, and I have this issue with my MacBook Air recently updated to Sequoia.

I back up the same MacBook Air at work on a Western Digital My Cloud NAS, and I have precisely the same problem.

I have the impression it is triggered when I leave the computer unattended (inactivity? Sleep?), even if in the Battery panel I have ON the switch "Prevent automatic sleeping on power adapter when the display is off".

I tried only once an overnight backup on an external SSD, and next morning I found the red dot with the "i" in the Time Machine control panel and the message "backup could not complete because some files are not available...etc."

Hope they fix it in 15.0.1/15.1.

Updating the SMB Service package to the latest beta (v4.15.13-2319) on my Synology NASes appears to have resolved the issue for me — at least for the time being.

After disabling the firewall and waiting for a successful backup to complete, I enabled the firewall again.

I was sure the next backup would fail, but it didn't and Time Machine completed several daily backups since.

Same issue: Mac mini 2020 M1, Sequoia 15.1, Synology NAS

When this still didn't work with the updated MacOS 15.1 and turning the Firewall off, I tried a different tactic.

I shut down the Synology NAS

In Time Machine I selected a manual back-up. Time Machine responded that it could not find the server.

Restarted the NAS.

Again selected a manual back-up in Time Machine.

After some time "preparing the back-up", the backup actually began....and completed!

The Firewall was active the entire time.