Time Machine backup on macOS Sequoia cannot be completed

I had this exact same scenario. After being on 15.3 for a bit, mine has resolved. No longer wake my machine to find the incomplete backup error.

OK, Nine hours is too long! Have you tried Disk Utility on the Time Machine disk?

Had same problem. Loged out and then loged in again while computer is running. Don't turn off and on. Since that everything have been working.

This was happening with me also. After looking at all of these comments, I was on the verge of purchasing a new backup drive. What I found worked for me was to reformat the backup drive, plug it into my 3 usb hub (instead of directly into the usb on the Mac Mini) and then set this drive up as the Time Machine backup drive. I have set it up to backup daily and for the last 3 days it is now working fine. I was previously under the impression that the Time Machine drive had to be plugged directly into the Mac. I guess now with Sequoia, it is best not to plug it directly into the Mac. As has been mentioned by many users, it was trying to do the backup but stop while the backup was in progress and eject the drive prematurely. I would get the warning that the drive was ejected improperly when Time Machine (or the system) was doing the improper ejecting of the drive. At least for now it is working properly. Or, at least I am getting backups. Hopefully, I won't have to test this any time soon.

Go to Settings, then select Time Machine, then select time machine volume. Hit the Minus (-) sign, and then hit the plus sign (+) to add it back to the same volume. I'm assuming you ran Disk Utility to verify it is a sound volume. This worked for me and I have tried most of the other methods without success.

Go to Settings, then select Time Machine, then select time machine volume. Hit the Minus (-) sign, and then hit the plus sign (+) to add it back to the same volume. I'm assuming you ran Disk Utility to verify it is a sound volume.

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.

After two rounds yesterday with Apple support, I was no closer to getting Time Machine to work on either of my Mac Minis running 15.1.1. Afterwards, I had an idea related to a similar issue I had with a Brio webcam a few years ago. I ran to Target, picked up a quality USBC to USBC cable and connected one of my USBC drives (each computer has multiple backup drives connected to it) directly to my M4 mini and ran Time Machine. It worked. At least it worked when I tried it last night. I have more USB-C cables coming in from Amazon today and will see if that makes a difference with the other drives. I will report back here to let you know what happens.

When my display is asleep and Time Machine attempts to run, it fails and presents the error message "Time Machine couldn't back up...". Waking up the display and manually selecting a backup results in success.

This bug has been reported for months in various other forums.

Yet another Sequoia bug...

"/etc/nsmb.conf" is not necessary. With "sudo sysctl debug.lowpri_throttle_enabled=0" alone, my Mac mini M2 needed 2 minutes for "preparing" and 3 minutes for backup and clean up (to Linux Samba server over LAN)!

Reference: https://mjtsai.com/blog/2016/03/16/massively-speed-up-time-machine-backups/

Update: Apple has since ghosted me for a second time despite having a customer service agent "dedicated" to my issue. Not the first for them....

Despite this, upgrading to MacOS 15.2 may have resolved? I'm not 100% sure at this point as I've had periods in the past where Time Machine has worked, only to stop days later. So far however, it has been about 5 days straight without errors.

After upgrading to 15.2 I did continue to get the errors, however I removed my two ssd's from Time Machine and I restarted my machine. I then re-added both drives and they continue to back up without issue, for now. Crossing my fingers.

On my M2 Macmini Pro after upgrading to 15.2 I also got the extremely annoying notifications every time I woke the machine. I noticed that after upgrading to 15.2 from 15.1 the firewall seems to now be enabled by default - it was off previously. I added /System/Library/CoreServices/TimeMachine/TMHelperAgent.app to the apps listed in firewall Options… settings and that seems to have resolved the problem.

After I removed the FindMy widget from the Notification center, TM backups while the machine is locked work fine again. I guess there is some permission issue to access FindMy widget info while the machine is locked.

Fons

I have experience with only one 3rd party backup software for the Mac, and it is Carbon Copy Cloner (CCC). I have used it since 2017 (v4) and it is now at version 7 since last June. Tech Support has been incredibly responsive the two times I contacted them. I strongly recommend it, although restoring a file is not quite as simple as in TimeMachine.

CCC is extremely customizable; I have weekly and monthly backup schedules for my M1 Mac Studio, my wife's MacBook Air, and two of my NAS servers. I could have it run daily backups on our two computers, but I still rely on TimeMachine for that.

I got CCC initially because TimeMachine, while it generally worked well for backups, going into previous TM backups to restore a file was agonizingly slow at times. And I relied on CCC solely for the 3 or 4 months between the release of 15.0 and mid-February when TM failed to consistently backup.

@ med8or: you can get this particular message if your internal drive is nearly full. Although TimeMachine backs up to an external drive, some space on your internal drive is needed to complete the backup