Time Machine backup on macOS Sequoia cannot be completed

This continues to be an issue for me and I have opened a support ticket with Apple. It has been escalated to their engineers. I have reinstalled the OS, the new 15.1 didn't resolve the issue, reformatted the drives, uninstalled the antivirus software I was using, and still have the issue. Interestingly, the backups were working again for the first few days of upgrading to 15.1 and then have stopped again.

I get no specific errors other than Backup Not Completed: Time Machine couldn't back up to....

I'll update this thread with any updates.

My Time Machine backs up fine until my iMac goes to sleep. Upon waking, I see the error message that it could not complete the backup. Then it backs up fine. More of an annoyance for me than anything, but something I hope Apple fixes. 24" M1 2021 running MacOS 15.0.1

All of these posts about deleting the default nsmb.conf file are completely irrelevant as backups fail whether backing up to a remote drive over SMB or over a local drive.

The problem is happening because Time Machine is being refused access to certain locked files. The specific files can be viewed by searching the logs for the last 24 hours or so:

log show --info --style compact --predicate '(subsystem == "com.apple.TimeMachine")' --last 24h

Time Machine should have full disk access so this is a bug in MacOS.

• I had no success backing up to my Western Digital (MyCloudEX2Ultra) since upgrading to Sequoia. Updated to 15.0.1 with same problems.
• I found an old post that suggested running this command in Terminal: sudo rm -f /etc/nsmb.conf (note: you may need to provide the password used to sign into Sequoia before Terminal will run the command)
• Since doing so, Time Machine has passed the prior errors and appears to be completing a backup on my MyCloudEX2Ultra via wireless network. As of this post, it reports 5 hours remaining (took <45 minutes to back up to a standard USB drive)
• Hope this helps

Glad it worked for you. Unfortunately, I did the same thing you did but still have the problem. I did remove my NAS drive from Time Machine, delete the partition on the NAS and create a new differently-named one, go into Safe Mode, added the new partition and successfully did a full initial backup. I then rebooted into "normal" mode and successfully did a 2nd backup.

But from that point on, if I am "actively" using my Mac, TM completes successfully. However, if I walk away and my Mac is idle, TM always fails to complete a backup, regardless of any energy, screensaver, "put my disk to sleep" settings.

I have nothing but issues with Time Machine since upgrading to MacOS 15.0 - was hoping it would be resolved under 15.0.1. Removing and re-adding the two APFS drives I have attached sometimes resolves the issues but eventually the error continues.

Time machine occasionally fails to complete its backup operations due to files unavailable error. Interestingly, it completes once I am active on the MBP M1 16" running 15.0.1. Not sure what I can do next to avoid the issue.

Yes - the problem is very much related to Time Machine losing permissions to certain files when the machine sleeps. I've worked around this (until it's fixed) by making the following changes to power management:

sudo pmset -b hibernatemode 0

sudo pmset -b standby 0

sudo pmset -b disksleep 1

What this does is prevent the machine from fully hibernating. This will affect battery life a little if it's a laptop you regularly take about the place, but in general terms this is how MacOS -used- to operate.

So I have been trying without much success to complete a TC backup until today. I've tried all the command line suggestions above, but today I tried using caffeinate without any flags in the terminal and the backups have all completed without any issue. So it may seem like it's an issue when the machine goes into sleep.

Just tagging in to say "same". Only when sleep. When awake again is fine. So would appear to be some state change in something(s) somewhere that blocks some process.

FWIW, this is to a Fantom Thunderbolt drive, not finding specs at the moment, APFS. Info shows as Bootable=No, Journaled=No, SMART=Not Supported,not encrypted,Ejectable=Yes. Looks like I have it hanging off a OWC Thunderbolt Hub USB4.

Note: I had Mac Firewall turned off. Will test later with firewall on.

Regarding my original post: I had Mac Firewall off when I applied the suggestion.

I, too have had problems with TimeMachine backing up to a Synology NAS server since upgrading to Sequoia (15.0 or 15.0.1, don't know which). Problem continues under 15.1.

I tried some of the other suggestions - (1) turning off Firewall, but (2)mainly removing the backup drive in TimeMachine settings, deleting my old backup folder on the NAS, booting into SAFE Mode and pointing TimeMachine settings into a newly created NAS folder share and backing up (successfully). Then doing a "normal" rebooting. Time Machine successfully backups as long as I keep my Mac Studio active. But whenever I leave my Mac and it hibernates, it always fails. But once I get back onto my Mac and it is "active", TM successfully backs up.

I have already gone into System Settings : Energy and enabled "Prevent automatic sleeping when the display is off" and disabled "Put hard disks to sleep when possible". This has not prevented the backup failures when I am away from my Mac.

I will try the suggestion above to change my power management.

I have a Mac Mini 2 with a Raid 1 WD My Cloud EX2 Ultra on my home network. Time Machine back ups worked every time until Sequoia 15.0 and same problem with 15.1. Can back up to an external HDD fine but to the EX2 Ultra is no longer possible. I have tried all the solutions offered on this forum which I am grateful for, however still no joy with EX2 Ultra. I hoping 15.2 will have a fix for this. Thanks to all for your suggestions.