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

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

Same issue here, usually making backups with TimeMachine to a Synology shared NVMe USB-C Drive without any problem. After upgrading to Sequoia 15.0.1 Final Release, TimeMachine crashes randomly seeing also High CPU utilization few seconds before. We have this enormous issue + Calendar Widget Language issue. This is the quality expected on a Final release?

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

Thanks but your suggestions didn't help other than it caused the destruction of the entire backups. So I guess there's no problem now since there's no backup left to worry about. Oh Well.

After destroying the backup, new backups fail during creation.

If you have anything important in your backups I'd suggest that you either don't update quite yet, or turn off TimeMachine then wait for Apple to figure out what they've broken and what they need to do to fix it.

When I start the backup with the firewall off, the backup to the synology NAS works fine, albeit very slowly.

As soon as I turn the firewall back on, while the backup is running, the backup crashes with the following message:

Time Machine could not complete the backup to 'TimeMachine_bck_share'

The network drive was disconnected from the Mac during a backup.

Make sure the computer and the backup drive are on the same network and that the backup drive is turned on.

The strange thing is that the Network Drive is just accessible.

But apparently not for the timemachine application.

For me it's nearly the same Issue on M2-Mini 15.0.1. Before the update, TM was working fine.

On my QNAP-TS221 NAS, a TimeMachine Backup (manualy started) stopps with Message 'Network Disc was disconnected during the process' after many many minutes. Before it was always in mode 'prepairing the Backup'.

The Firewall on the M2 is and was always OFF. So this trick, didn't work for me.

Now I tried to just copy some files (25GB) to the NAS Share. The first attempt also stopped after some MBs without any message. The second attempt, during the MB Air was doing his TM-Job, now finished completly fine. After that, i tried once more to start a TM-Task on the M2, but stays still endless in 'prepairing the backup' mode.

On my old MB Air (MACOS 11) the TM-task seems to work fine, although very slow (more than 1h for 40GB, but it's on WiFi )

Is this Community here, the right place to tell apple about this problem? Or should we place it somewhere else?

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 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!