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

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.

[Edited by Moderator]

That isn’t what I posted. You need to get spotlight to reindex.

to do this add the main hard drive to the Spotlight ignore list, wait maybe 30 seconds and then remove it. This will start Spotlight reindexing on the drive.

You should be able then to check this by opening Finder and viewing most recents, you should see that list starting to populate.

Once that is there TM backups should now work with the Mac locked.

If your backups are screwed you may need to reinitiate them. Hopefully though you should be good after that is done.

The reinitialisation of Spotlight indexing, after 2 attempts is working this morning. I'm keeping my fingers crossed that this will continue work. But I have had intermittent Time Machine performance before, using other methods of remedy. Thank you for your suggestion.

Well my TM machine backup failed again tonight. Reindexing is not working for the long term. But a restart will always get it working again. Just installed OS 15.1.1, which included the usual restart. TM working again and will see how long it keeps working now.

I spent time with Apple Support — supposedly a Mac Senior Advisor — who basically had no real answers to my questions:

[1] He did not commit to say that turning the Firewall would continue to be a workaround for 15.1.1 as it works for me in a MBP 2021 M1 Pro and 15.0.1.

[2] They are still investigating the issue with 15.1.1 and do not know if and when the issue will be resolved. I pressed onto the Senior Advisor that issues with Firewalls and Time Machine were not minor and Apple should not sweep them under the rug. Again, no commitments from the SA.

[3] I filed a complaint that one of the Advisors (first level support) insisted that I upgrade to 15.1.1 and then contact them again if that did not fix the issue. My bone was that I would not do it if it meant that “my” workaround (turning off the Apple Firewall) would not work. They could not answer that.

Has anyone here using 15.1.1 tried turning off the OS Firewall and testing if the backups complete without issue? Or they are are also failed?

Okay thanks I'll format the external drives and wipe the NAS partition then before going through with the procedure.

You do not need to wipe out the NAS partition. It works if you just delete the appropriate sparse bundle.

Also, make sure that you don’t turn on the Firewall again.

Does anyone know if Apple fixed this problem in the upcoming Sequoia 15.1 update?

Eh..... turn off the Firewall? Why? Are there issues with it?

I would have thought it'd be a major security issue if it was turned off?

Indeed I do!

Heck I'd not heard of it causing issues (or causing this one), is it a known issue?