Time Machine backup on macOS Sequoia cannot be completed

I think this started with version 15.0 but it may have started earlier. It is a nuisance more than anything. We have two Mac Mini M1 computers that were purchased and set up at the same time to be identical. TM throws an error on one computer if the user is logged out or if the screensaver is running. Both systems are set to not sleep the hard drive and to wake for network access. Both systems have always had the Apple firewall and file vault enabled. Neither system has ever used any anti-virus or anti-malware software. Both systems hide the IP Address and the email address. Both systems run the same adblocker. Both systems share the same family icloud plan. Each system shares data with identical iPhones. Both systems use rotated external Seagate USB hard drives for the TM backups; and TM fails on the one system with every external HD I have ever connected to it every time it is unattended. There are some extra applications on the system that has the TM problem: FitBit Finder, HealthRate, Prime Video, Klondike Solitaire, Speaker Connect and TurboTax.

You might want to pass on the info to Apple Support that "no longer supports obsolete technology", this way we can all benefit from the workaround...

FYI this is what they suggest as workaround:

Back up your Mac with Time Machine - Apple Support

Although I have heard somewhere that Time Capsule is no longer supported, it isn't true that you cannot back up wirelessly or via ethernet when running Sequoia. My MacBook Air does this every hour alternately to a Time Capsule, then to a WD NAS. It isn't reliable in that if my MacBook Air goes to sleep, the backup may fail. I cannot tell if it always fails.

When will Apple fix the OS such that when the display is off, Time Machine backups run and are successfully completed? I don't think it's a display problem as I'm using a Studio Display and wouldn't think an Apple product would exhibit such an incompatibility. Plus, it worked fine up until Sequoia.

I didn't know that some consider Time Machine to be on its way out. I will continue using Time Machine but considering also having a second backup strategy/program. Any suggestions or discussions about "best alternatives"? Thank you.

Every once in a while, the TM backup of my MBA finishes without error message. So, it took me about 2 weeks to get a fresh backup on a new TimeMachine disk after I had dropped the old one to a hard floor while it was connected, which killed the drive.

More important though, all my files and documents I work on are backed up despite the error that the TimeMachine backup could not be finished. So, I am not concerned any more, I close the error message and continue working. I think, I simply don't need a finished TimeMachine backup, as all I need is my current files history on my TimeMachine disk. Which it has.

So, the message is: Don't be concerned about the error. The system will have your files back up. If you need to recover a Mac from the backup, I would think that even that would work, as long as you have at least one backup that completed.

I am seeing that this thread goes back to Oct 2024. I can't believe Apple doesn't have this sorted out with the new 15.4.1 update!? I updated and actually the Time Machine issue only got worse in my experience.

Have read most of the posts. Now running 15.3.2 and having this problem - except it's there even when the machine is awake. The problem file is buried in MS Word Contents. I changed its permission to ReadWrite. No help. I deleted it and emptied the trash. No help. Same file is the problem even though it no longer exists.

Exactly the same. It gets worse with every Sequoia update -- also, my TM frequently gets hung up even when my MB M3 Pro is awake, such as right now, stuck at 65.9% for the last ten minutes. Next, it will tell me "Backup Failed" and disconnect my Sandisk TM backup drive.... yup, just did it. (Apple, please refrain from blaming the drive. It also happens with my alternate TM drive, a Silicon Power 2TB Bolt B75 Pro External SSD.) Please fix Sequoia -- and don't get me started on what a mess it's made of Apple Mail, which often has to be force-quit to download new mail. Steve Jobs would never have let profit take priority over quality. For shame.

Time Machine backups stopped working after I updated to Sequoia 15.4.1 in April 2025. I noticed just recently that my Time Machine backups had stopped. The date of the last successful backup seems to coincide with the date i upgraded to Sequoia 15.4.1 on April 16 2025. I have had two calls with Apple tech Support attempting to resolve this issue with no luck. I believe the only solution to fix Sequoia. What I would like to know is - Is fixing this problem on the list for Sequoia 16?

I get the occasional file that TimeMachine won't back up and it is usually a file in Notes.

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.

what does sudo rm -f /etc/nsmb.conf really do

How to disable SMB 1 or NetBIOS in macOS

How to disable SMB 1 or NetBIOS in macOS - Apple Support (CA)

Would you post how you determine that the file not being backed up is a Notes file? The error I see on my MBP when Time Machine fails to complete doesn't specify which file is problematic.