What causes Time Machine to stall during backups?

It's just lazy customer support to ask users to wipe their TM drive and/or Mac hard drives (and restore or reinstall macOS). There is obviously a NEW bug in macOS 15 that is causing this when TM kicks off and the screen is locked. Obviously. Wiping everything only papers over the problem and DOES NOTHING to find the real issue.

I say "lazy" without any guilt. I do customer support for a software company and I always want to find the real cause rather than paper over it. Look how many people are impacted by this!!! The real number is 1 or 2 orders of magnitude more! (because people don't spend the time finding a place to post their problem)

I'm very sorry to say but the 'fix' didn't work for me at all. I went through all the steps in full, and this morning after being out for a walk, with the Mac locked I returned to find the errors were back!

Exactly the same situation, 'some files unavailable' so the backup could not complete.

Now I'm working on the Mac (that is it is unlocked) the backups are now taking place and completing without any errors.

Apple need to fix this issue.

..... And I can confirm the issue was fixed after the restore, but that was on macOS Sonoma, as soon as I uplifted to Sequoia the issue returned, as I expected.

I've just spoken to Apple Support again and she is going to investigate and cal me back tomorrow.

If it is any use to anyone my case is 10*******93.

If you have reported the case and have a case number please feed it back, as she did indicate she was not aware of any other reports. If you have not reported it please do so and feel free to reference my case number.

The more of us that report it the quicker it will get resolved.

[Edited by Moderator]

I'm having this issue, or one quite similar. I get the same error message "Time Machine did not finish backing up because some files were unavailable. Backups will resume when your Mac is unlocked."

I last Friday I migrated to a new M4 Mac mini, now running OS 15.1. That went without hitch. I took over (captured? whatever the term is) the old TM backup, and that seemed fine too. Backups happen on the regular TM schedule, but sometimes I do get this error message. When I do, if I manually trigger a TM backup, that takes place without incident. I just returned home after being out for a couple of hours. Screen was locked and mini was locked; my AppleWatch unlocked the mini. I see that 20 minutes ago a TM backup too place. So this problem, whatever it is, is not even consistent for me.

I found this on reddit:

log show --info --style compact --predicate '(subsystem == "com.apple.TimeMachine") && (eventMessage like[cd] "Failed * acquire device lock assertion*")' --last 8h

to find the file. For me (and others on reddit since macOS 15.0):

Timestamp               Ty Process[PID:TID]
2024-11-15 17:02:28.528 E  backupd[322:533fa9] [com.apple.TimeMachine:FileProtection] Failed to acquire device lock assertion for '/Volumes/com.apple.TimeMachine.localsnapshots/Backups.backupdb/max/2024-11-15-170051/Data/Users/xxxxx/Library/Containers/com.apple.findmy.FindMyWidgetItems/Data/SystemData/com.apple.chrono/snapshots/com.apple.findmy.FindMyWidgetItems/systemSmall---4259486853547037044----164.00w--164.00h--20.00r--0f--0.00t-0.00l-0.00b0.00t.chrono-timeline' (assertion state: <dropped>), error: Error Domain=NSPOSIXErrorDomain Code=1 "Operation not permitted"

Really seems like a new bug, Apple. Stop telling people to wipe their machines!!! Ask them for this info!!!

I am seeing this error after updating to Sequoia, too, but I'm not interested in completely erasing and reformatting my backup drive yet because I'm hoping for a real fix. I'm currently running 15.1.1 on a MacBook Air.

I've had some success with backing up either while I'm actively working on my Mac and thus keeping the hard-drive active or changing System Settings>Time Machine>Options>Back up on battery power>Off and System Settings>Lock Screen>Turn display off on power adapter when inactive>"For 3 hours" or "Never" when I want to be backing up. This seems to prevent the computer from locking, which is what the error message seems to be suggesting is a problem. I'm lucky because I work from home, so if my computer sits unlocked for awhile it's not an issue. But I have to remember to reset the Lock Screen setting if I'm taking my computer someplace where the lack of security would be an issue. This is an inconvenient work-around, but at least I'm getting backups done, for the most part, until Apple actually fixes the problem.

The latest things I'm trying:

• Emptied the Trash Can
• Rebooted the Mac
• Wiped and formatted my TM backup drives (emptied the NAS TM share)
• Set TM up to backup to external drives only (for now I've ignored the NAS share as it's slower)
• [Still got the TM errors up to here]
• Forced a Spotlight reindex (again)
• Went into TM settings and excluded all external drives from the Backup
• Went into Spotlight Privacy and excluded all external drives as well as network shares from being searched.

So far four TM backups with the Mac locked with no issues.

After I updated to 15.1.1 that is when the backups broke again.

hi again, mr. luigi. i don't know if this will help anyone else, but i use an app called TimeMachineEditor (free at https://tclementdev.com/timemachineeditor/) to schedule my once daily backup at 4:00 (a.m.). again, i don't know if it'll help anyone else, but since i have a working (at the moment) system, i'll share whatever i have.

To update....... the issue was still there with 15.3 .....

After a number of weeks with me updating Apple Support with things I'd tried (which worked for a while) and then failed again ..... and getting no reply back at all. I went through the pain of calling them again and complaining about the lack of a response.

Finally, I got it bumped to a 'new' top level support guy.....

He investigated, said it wasn't a confirmed issue, but did say to triage it further was I in a position to wipe the TM backup drives, wipe the Mac Mini and rebuild it manually (no TM restore).

As I'm retired that would be painful but not impossible to do. I'm now at the stage the Mac has been rebuilt, most of my essential apps are loaded, a new TM backup has been set......

So far it's all been running 5 days, 4 hours, with not a single TM backup problem.

I'm continuing to add apps daily, and I'm logging the install times of each, just in case the problem returns after an app is added in.

Anyway I thought you guys might appreciate the update. I'll keep everyone posted.

Guys yesterday I realised that Spotlight was not indexing things properly on my Mac. I then followed this support article, and added / removed the hard drive on the Mac as well as excepting a few drives.

This morning I accessed the Mac and I had no TM backup errors at all. W00t!

So is it worth you guys reinitialising Spotlight and seeing if it fixes your errors? Worth a try!

I'm curious about the solution. I've the same issue which has occurred from Sequoia 15.0.1 onwards (now running 15.1). This is on a Mac Mini 2 Pro.

I have three TM backups:

• external drive (via USB-A hub)
• external drive USB-C
• To a share on my Synology NAS

It looks like the solution involves getting the Mac into save mode and then reconnecting TM. I wasn't sure that was possible for the network share to the NAS, but if it is…

Then the big question is… when re-adding the drive into TM, what do you do with the existent TM backup, re-use it, or start again with a fresh backup?

I'm assuming here that for the NAS, the existing bundle in the share needs to be deleted from the NAS side of things?

Any further thoughts or info would be appreciated.

Have you tried reindenting Spotlight as I advised up thread? It solved the issue instantly for myself and my wife?

Same errors after getting around the Firewall issues brought in with MacOS 15.0.1 on a MacBook M1 Pro. This is a disaster of an update by Apple. The issues with Time Machine because of the update are not acceptable. Still, Apple support has not provided any solutions.