Since update to MacOS 15.0.1 Time Machine backups do not work

So here's more information from my side.

I use TimeMachine as a convenience, not my only backup option. I've been to this rodeo before with Apple and TimeMachine.

My system wasn't failing to connect to the Synology or the backup data. Everything connected fine. The backup access was long enough to copy 6.5 MB then failed.

After forgetting the target disk and reconnecting it, the OS properly recognized that a prior backup existed, then asked if I wanted to delete the backup history, which sounded like it was different than the actual backup itself. I thought it was just going to delete all the indexes to the backup data and that during the backup process those indexes would be recreated. My Bad.

While fiddling with it a bit more I was watching connections to the Synology.

The Backup starts, creating one SMB3 connection to the Synology.

Then about 5 minutes in, while the TimeMachine application in Settings is still doing the "Cylon bar" & Preparing the backup. There's another SMB3 Connection made to the Synology.

About 90 seconds or so after that, the newer connection is closed.

A few minutes after that, TimeMachine reports that the connection to the backup disc was lost and that the backup failed.

I'll let Apple worry about it. I've spent way too much time over the years being an unpaid Software Quality Assurance person for them. I am a career SQA guy so I'm a bit mercenary about it.

I reported it so that other people who might rely on TimeMachine didn't lose their minds, or their data, trying to fix a problem Apple introduced with 15.0.1

Apple broke it, it's their backup system, it's their OS, they can diagnose and fix it.

I'm having the same sort of problem. Verification of the backup also fails with the same message.

I get the following message using a Synology NAS.

For me, the backup fails at 6.5MB every time. That's what led me to trying a backup verification.

The NAS itself is functioning just fine.

Looks like Apple broke something. If you haven't updated to 15.0.1 you might want to hold off a bit.

Mackbook Pro M2 2023

This is an unbelieable bug that should not happen.

How come an udpate is not tested in such a configuration that is so common.

Something is not working at apple software quality assurance

Seems to be a MacOs Sequoia Firewall Issue! please try to deactivate temporally the Firewall, and force a Timemachine Backup (don't forget to reactivate firewall when your backup finishes), so have to wait unti Apple fixes the Issue with the Firewall

I am currently having this issue with Time Machine and my Synology NAS. 15.2 did not fix it. Turning off my firewall to do a backup does not work. I did not change anything in the NAS setup. It just went from working to not working. I get this message from Time Machine.

Note also that I can no longer add a drive for TM backups. I get this message:

Oddly enough, I can surf the NAS in Finder with no issues. It mounts OK and is available as a shared drive on the network. Again, this is all new since Sequoia, it seems.

One more note - during the connection process (that usually fails) TM is able to correctly show the available disk space on the NAS drive. It takes a while but eventually it fails.

Sad to report that Sequoia 15.1 does not change the problem for me. I reliably get the failures with firewall on, and never with firewall off. My backups are from a MacBook Pro M3 Max (Sequoia 15.1) via TM to a networked Apple Mini (Sequoia 15.1) with two hard drives connected via USB to the Mini.

Sequoia 15.1.1 also did not fix the problem for me. Note that my configuration is all Apple (MacBook Pro to networked Mini to its attached HDDs). TM backups work with MacBook's firewall down, fail with it up. Apple definitely owns this one.

And it gets worse. I'm running 15.1.1 on M2 MacBook Air into a home-brew Ubuntu server with Samba and Time Machine settings. It's worked for a few years quite reliably. Now it stopped with 13% done claiming out of disk space (wrong because TM manages disk space through quota settings on the server). Before I read this thread, I did the usual fix of forgetting and attempting to reattach the TM share; failed big time because I can't modify the Registered User name and can't type more than one character of the password. I've tried the shields (firewall) down approach with no change.

Apple you've really messed up this time.

I wish I found this thread a two weeks ago, but I have some good news. After struggling with this for days, I contacted Apple. After days of back-and-forth calls with them, my third Advisor confirmed that in macOS 15.0.1 they introduced a bug in the Firewall feature, that they are working on a fix (hopefully a soon-to-be released 15.0.2), and there is no setting that we can make to create a firewall pinhole (which I asked for).

In the meantime the recommended work-around is to set Time Machine backups to be manual (not hourly or daily), to turn off the Firewall when ready to do a TM backup, manually kick it off, and (when it is done) to turn the Firewall back on. Effectively, we have to "lower shields to use the Transporter" (Trek fans will recognize the analogy). It sucks, but at least it gets the job (sort of) done.

I would recommend, before you run your next TM backup, you "lower shields" (Firewall) and option-click on the TM Menu Bar icon to run a Verify process to be sure that this problem hasn't corrupted your TM backup. After this happened (on October 3), my TM back up was corrupted and I had to start over (twice or three times during the debugging process).

[Edited by Moderator]

This is really good news, but I since I am seeing more such issues related to broken connections, I hope Apple will not set a focus on TM but on the general underlaying problem.

for example I was using a remote session to an lab environment with Chrome and the connection was broken in random intervals! After a while I remember weed the TM issue and turned the local firewall off. After this change I did not face any connection related issues anymore.

Thank you. At least they didn't break it further from 15.0.1 vs. 15.1.1.

No one at Apple has apparently tested it because they could not answer the question you have answered for me. I will consider doing the upgrade and continue to use the workaround of the Firewall down. Apparently, the one with reindexing does not work any more with 15.1.1.

Best regards,

M

I have exactly the same error when backing up to my NAS since installing the 15.1.1 Update. Prior to that I've not had any issues with Time Machine backups. The NAS is working fine, and there were no other IT changes.

I've scoured the various forums for a solution but have not found anything that works. I've resorted to backing up my iMac to a USB external until Apple figures this out.

There is the perfect word in German to describe Apple's problem with MacOS 15.x and Time Machine on an Apple Airport Extreme: "Schlimmerbesserung" (which loosely translates to worsened improvement).

15.0.1 required me to completely wipe and restart my Time Machine from scratch.

15.1 no joy, several disconnections and "Time Machine full" warnings

15.2 worked (sort of) but started slowing down the entire machine (making it feel more like an Intel driven machine rather than an Apple Silicon driven machine)

15.3 has blown up to over 700% CPU, and essentially grinding the machine to a halt requiring a Force Quit on diskimageiod to get anything to work on the machine (multiple times through the day).

Is there a workaround or do I need to stop using Time Machine (this problem has now existed for over half a year with Apple not fixing the underlying problem of limiting CPU usage for Time Machine).

Confirm. After disabling the firewall, the backup will run smoothly.

This option works for me too.

But it's happening since the update to MacOS 15.0.1. So Apple should fix this problem I think!