Time Machine backup on macOS Sequoia cannot be completed

Update, though probably not helpful. I called Apple again tonight and learned it was an active issue, hopefully solved with next update. In the meantime, they thought it might be a lose cable to the HD - however the same thing is happening on my brand new M4 machine. I went out tonight and purchased a USBC to USBC cable to connect by backup drive directly to the USBC port on the M4. It's the first backup (since it hasn't been working), so there's an hour to go before I know if it works. The Apple rep didn't think there was much chance that would help, but I wanted to see - thinking it might be a power issue to the backup drive. I'll let you know if it works.

I have 5 TM backup volumes. 3 work well, all locally connected via OCW TB4 hub and USB3. The oldest local one began to give the "disconnect" error message 3 days ago. No firewall.

Macos 15.1.1, M2 MacBook Air

No automatic sleeping on power adapter when the display is off.

Attempted interventions that had no discernible effect:

Reboot.

Log out, log back in with machine continuously running.

Removed then replaced backup volume from list of backup volumes.

Switched out USB3 cables, switched connection from USB3 hub to TB4 port on Mac.

Apple Senior Advisor had me power down the computer, disconnect all other external volumes, and reconnect TM target to the OCW TB4 hub. This was successful.

The other failed TM volume was accessed via ethernet not WiFi network. It was giving an error that another computer was writing to it. This was not true. None of the relevant interventions above made any difference. Apple Senior Advisor had me verify latest firmware on the Time Capsule, and power cycle both the Time Capsule and the computer. This was successful.

I post this in the hope it will help some of you.

Prime Video is one of the culprits I’ve identified - it creates a login token which requires admin rights to access - I.e. biometric authorisation. Time Machine obviously doesn’t prompt for auth while the screen is locked and the backup therefore fails.

ultimately, this is a simple issue - the O/S is allowing applications to set access permissions which Time Machine can’t access without authentication.

My experience jives with yours. The critical condition which determines whether the backup goes through or not is whether my MacBook Air is asleep or not. I have multiple NASes which TM is tied to and each and both fail when hibernated, but succeed otherwise. I suppose the null hypothesis is whether there are any successful backups when hibernated, but I cannot tell. I am reluctant to throw in the multiple workarounds suggested because of unintended consequences, especially after Apple sends the next update, and I would not know how to undo the patch.

That TM predictably fails when hibernated, and predictably succeeds when not would suggest that is the salient difference and needs to be addressed in the TM code. When hibernated, there seems to be no reason to back up more than once since there is no activity which would change the contents of the disk, but it would be useful to allow the first backup or an ongoing backup to complete to capture the last changes.

My problem may be slightly different, but related certainly. In December I bought a new Crucial X9 Pro 4Tb SSD to replace a 2 Tb Time Machine drive that was complaining of being overfilled. I’d never had any problems with the 2 Tb Samsung. But after 2 months of daily Time Machine backups, the new Crucial stopped mounting completely. Disk First Aid could see it, but not mount it. This was after upgrading my M1 MacBook Pro from 15.3 to 3.1. It reported I/O errors and invalid object map on the APFS volume and also failed on the container disk. I reformatted again as APFS and the new disk passed all DFA tests, but the same errors, although not the failure to mount, were back after only 3 daily backups. Crucial tech support claims that this is a frequently reported problem with drives from multiple vendors under Sequoia 15.3 and recommended reformatting as exFAT or HFS+. I’ve reported the issue using Apple's Feedback Assistant app.

In energy setting, I have prevent automatic sleeping when the display is off, and manually turn off my two displays. In the past I was locking the screen. I'm not doing that. My hard disk is set to not turn off also. So far that is working and I'll see.

One way on my TimeMachine that it seems to stay connected is encrypt it and have the password set in the Keychain.

Get Drive DX and see what that reports.

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.

Time Machine IMHO is VERY basic backup system! Throughout its history every Mac new Mac OS updates it will Startup a new backup each every time! You better off with your choice of shareware backups that continue though at least two backups until a new version come out and pick up where it left off before the upgrade!

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.

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.

Similar issue here, Time Machine Backup fails after 15.0 update. My TM drive is inside a 2012 Mac Mini (Catalina) on my network. It has worked pretty much without issue for many years until now. Error message is "Time Machine couldn’t complete the backup to XXX" and then "The backup disk image was ejected or disconnected from your Mac while backing up." Of course the drive was not ejected or removed as it is internal to the Mini. I tried the Terminal command fix and it did not work. Time Machine attempts to make the backup, finds the changes, starts copying files and then displays "11.7% done - Calculating time remaining, Zero KB copied." Then that fails and the error message is generated.

My wife's Macbook Air which is on Sonoma not Sequoia, still makes backups to the same Mac Mini, to the same internal drive (different partition) without any problems. So this is without question a Sequoia problem.

Been thinking about getting a new M4 Mac Mini to replace the 2012. I use it for all sorts of home server tasks including hosting Time Machine drives. I hope Apple gets the bugs out of Sequoia soon.

It’s not the cables.

start a backup running and then lock the screen and leave it to finish. It won’t.

the problem is very simple - Time Machine is denied access to some files while the machine is locked and so cannot complete the backup until the machine is unlocked.

the problem is not hardware related as it happens with external disks -and- network storage.

Well, I have tried several suggestions posted on this thread, but ultimately none of them worked. I still cannot get TimeMachine to perform automatic backups when I am away from my computer (Mac Studio 2022) to my Synology NAS drive.

1) User Zoid85 suggested using a 3rd party app from the App Store called Coca. It initially seemed to work for me initially, performing backups the first night after I installed it. But after 24 - 48 hours, TM started regularly failing when I was away from my computer for significant portions of time.

2) User Chewbury listed three terminal pmset (power management settings) commands. They did not work for me. Then I dug into the pmset flags and options. The -b flag apparently affects only computers running on batter power (i.e. laptops), which does not apply to my desktop computer. The flag -c is for computers running on AC power, and -a appleis toall computers, regardless of power source. Using those flags, the three pmset commands still did not solve my problem. Looking at the individual settings pmset controls, I then sequentially enabled/disabled three settings (disksleep, sleep, displaysleep) both individually and in every possible combination. None of those solve the backup probram.

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