Time Machine did not finish backing up because some files were unavailable. Backups will resume when your Mac is unlocked.

I'm running 15.1 here and still have the issue. Unless you mean the forthcoming 15.2 update?

Where do you turn off the firewall? Running Sequoia 15.1

Have you tried the Spotlight reindex fix I suggested?

You'll lose nothing and it’s now worked for myself, my wife and a friend.

This did not work for me.

Temporally I would predict. Please tell me this was a permanent fix please.

Which one, the reformatting of the TM drives or the reinitialisation of Spotlight indexing?

This is interesting. No Spotlight and you have TM issues. Just a shot in the dark, but have you tried reindexing anyway?

沒錯 我剛剛也是閃爍很久 不過是i4

This procedure worked fine.

I also tried another one with my NAS: I rebooted the Server and the Mac and requested another back-up. For a while the error message for failed backups persisted but when opening the TM Settings, I noticed that the NAS disk showed the time of a backup without a warning attached to it. After the second or third backup to the server, no failed backup messages showed up. It seems that it is all is well now.

You still have the Router firewall (most come with protection software, including a Firewall).

The TM back up will complete normally if you turn of the Mac OS firewall. Otherwise, you will continue to have issues.

I meant 15.1 which is out for doing the upgrade. So, I am going to wait and see if 15.2 has the fix. I am getting tired of these constant upgrades which change settings behind my back and clearly are not sufficiently tested. Having back up issues with the firewall is not a minor inconvenience. Bad Apple.

I just reported the defect you see with 15.1 and the one I saw with 15.0.1 with Apple Support. If you do, they will give you a case ID number and you can inquire with them when an update comes if it addresses the issue using the case ID number.

I am sorry to hear that the solution was to wipe out your hard drive and restore from a previous backup. So, I guess that you are now back in 15.0 which showed no issues with TM for me.

Yes so I ended up wiping the Mac and doing a restore from a backup. I got a conflict when restoring which I ignored.

So yep it didn’t restore properly so I’m doing it again this morning. Interesting when it downloads the OS to do the reinstall it uses Sonoma.

So while the OS part of the restore is taking place it’s our early doors for a coffee.

I will be going back to using Sequoia even if it has the problem again so I can feed back to Apple. I know from past experiences cases are help open for 30 days.

I reported it for both 15.0.1 and yours @dbrewood for 15.1. No point of putting my case ID number as it will be edited out in accordance to Apple’s terms and conditions for using the Community site. I guess that they do not want to accept that this is, in my opinion, major as it compromises two basic functions of the OS: TM backup and firewalls. I will not update to 15.X until they fix this issue. I have two other computers around and they will remain in Sonoma now that one cannot download 15 but just 15.1 which is busted.

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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.