What causes Time Machine to stall during backups?

I've had no trouble with Time Machine until updating my Mac Mini M2 to OS 15.0.1. After the update, I constantly get the message "Time Machine did not finish backing up because some files were unavailable. Backups will resume when your Mac is unlocked." The backups seem to run fine until reaching about 80% then stall before the message appears. I've tried different ports, different USB C hubs, different cables etc. with the same result. I've scann the resources here and found nothing current or helpful on this issue.


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Mac mini (M2, 2023)

Posted on Oct 25, 2024 5:25 AM

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Posted on Nov 15, 2024 5:47 PM

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)

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Nov 23, 2024 2:52 AM in response to Kerry Kinkade

Following the changes made yesterday:


  • ........
  • Forced a Spotlight reindex
  • 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.


TM backups have been working perfectly every hour with no errors at all.

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Feb 17, 2025 3:31 AM in response to Kerry Kinkade

Another update guys.... since updating the firmware on the Nanoleaf lightstrip the 'Tile' on the iPhone has stopped giving any error messages and is working perfectly. So yesterday I put the Home widget back on the Mac desktop and configured it only to show the lightstrip and a smart plug.


So far the TM backups have been completing with the Mac locked or unlocked with the Home widget in place. I've done a lot of backup tests (Mac manually or automatically locked).


TM has been working flawlessly for 3 days, 23 hr, 40 min, and good since the Home widget was put back on the desktop 15 hr, 54 min ago.


It is still early days and I'll continue to monitor.


It is interesting to note though that my wife has had the same TM backup issues on her iMac, with the errors hitting her daily. I did reset her TM backup a couple of days ago but typically that only helped for a day or two. Since updating that firmware she has not had the TM backup error either. It could be pure coincidence but......


It does seem to make me think that it could be logical that (in my case at least):


  • The Nanoleaf firmware being out of date was causing an issue within HomeKit
  • That Homekit issue was common to the network and hence affected my wife's machine.
  • Resolving that issue fixed the problem on both machines.


So do you guys have any Nanoleaf (or other) products sat in your Homekit systems where firmware needs updating? It might be worth checking.


As always any feedback appreciated.

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Mar 23, 2025 4:40 AM in response to Kerry Kinkade

The error returned yesterday after 37 Days, 5 hours, 3 minutes of no issues.


I then carried out:


  • Quit out of Apple Books which I'd started using again earlier in the day, and had imported some ePub books
  • Reformatted an external derive I use for Carbon Copy Cloner backups on some files from my NAS, as CCC reported the drive was full.
  • The 'Use iPhone Widgets' on the Mac was turned off again. After the latest MacOS update it had turned the option back on.
  • Emptied the rubbish bin
  • Rebooted the Mac


Everything seems to be backing up normally once more.

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What causes Time Machine to stall during backups?

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