What causes Time Machine to stall during backups?

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?

Go into the TM settings use the options button to choose disks to ignore. Add the main hard drive on the Mac, wait 30 seconds and then remove it. That should force the indexing to reinitialise and solve the problem. Fingers crossed.

I resolved the issue after working with an Apple support person. I have an MBP M1 Pro with MacOS 15.1.1. and I had failures with TM both on NAS and hard wired backups. My workaround, as per the boards, was to to turn off the MacOS Firewall to let the backups work to completion.

However, I also have a cyber security software which includes a firewall of its own. There is a conflict between its firewall and the MacOS one starting with Sequoia 15.x. After I turned off the security software firewall and left the Mac OS one active, all TM backups work without error. The 3rd party cyber security software firewalls need to be updated for Sequoia.

I resolved the issue after working with an Apple support person. I have an MBP M1 Pro with MacOS 15.1.1. and I had failures with TM both on NAS and hard wired backups. My workaround, as per the boards, was to to turn off the MacOS Firewall to let the backups work to completion. The issue with the lockup screen seems related to the security issue I was seeing.

However, I also have a cyber security software which includes a firewall of its own. There is a conflict between its firewall and the MacOS one starting with Sequoia 15.x. After I turned off the security software firewall and left the Mac OS one active, all TM backups work without error. The 3rd party cyber security software firewalls need to be updated for Sequoia.

Interesting. Arq Backup started having a problem with a file similar to that as well. Excluding ~/Library/Containers/com.apple.findmy.FindMyWidgetItems/Data/SystemData/com.apple.chrono/snapshots allowed it complete.

I resolved the issue after working with an Apple support person. I have an MBP M1 Pro with MacOS 15.1.1. and I had failures with TM both on NAS and hard wired backups. My workaround, as per the boards, was to to turn off the MacOS Firewall to let the backups work to completion.

However, I also have a cyber security software which includes a firewall of its own. There is a conflict between its firewall and the MacOS one starting with Sequoia 15.x. After I turned off the security software firewall and left the Mac OS one active, all TM backups work without error. The 3rd party cyber security software firewalls need to be updated for Sequoia.

The 'issue' came back for me this morning. So instead of my usual 'fix routine' (emptying the trash can and reindexing Spotlight) I've added your exception and we'll see if it fixes it!

Fingers crossed!

I just added the M4 Mac mini to my NAS backups and I am getting the same issue with 15.2. Tried all the solutions here and the issue comes right back. I have a M2 MacBook Air that uses TM to the same NAS and it has no issues, settings are the same so not sure what the issue is. Backups are too important for me, unless Apple fixes this issue I'm going to be using an alternative to TM (most likely Arq) just to much time wasted trying to work around these issues. Starting to feel like a windows user.

I've given up on Time Machine. Far too many problems over the years. I've lost all my history three times so far. After upgrading from macOS 14.7 to 15.2 Time Machine started failing. It would stall/fail during the night trying to complete a backup. No idea why, no idea how to fix it.

Then Time Machine deleted over two years of history! Now that everything is lost (again), I reformatted and tried with a clean drive. Again, failed during the nightly backup. This happened two years ago, and then I lost about three years of history.

Sure, clicking "backup now" would complete a backup but here's the question: How do you know it really worked? Have you tried to to restore? Even when it completed the backup I find many errors in the logs. I find the same errors many other have reported with macOS 15.

So...I do not trust Time Machine, and after so many years of losing backup history I'm done forever.

Now I'm using Carbon Copy Cloner to create backups. Works really well, twice as fast, and does everything Time Machine ever promised and much more.

with your experience, i can't say that i blame you for not trusting the backup. however, every time i've needed to recover a file or file system, the backup was there. now you've got me scared. thanks for nothing :-) (that's supposed to be a smiley face). after taking part in this discussion, i'm going to have an alternate backup system ready to go.

Hi bruiselle! I wanted to report back on my experience directly plugging my two backup HDD into the M4 Mac Mini. Since I already have used two of the Thunderbolt 4 ports in the back of the Mini, I could only plug one of the backup drives into the back of the Mini. I plugged the other backup HDD to one of the 3.1 USB ports in the front of the Mini. I woke up this morning to failure again. I am going to try one more thing. I removed the backup HDD that was connected to the front of the Mini and also removed it from the list of backup drives for TM. So now I have only one backup TM drive and it's connected to the back of the Mini via a Thunderbolt 4 port. Let's see if this works. I prefer two backup drives, but if this works, I'll go with it as I also use Dropbox and Sync for all my documents, etc. BTW, when you said you solved the problem by directly plugging your backup drive(s) into the Mini did you mean using the Thunderbolt ports in the back?

I'm reposting the following comment for historical purposes as it was accidentally deleted by the moderators due to a miscommunication. It was originally Posted on December 29th.

Hi Folks, I bought my wife an M4 Mac mini for Christmas and have it all set up. As for background, I set it up from scratch as a new machine. It is running MacOS 15.2. In general, the new Mini is running fine. Unfortunately, she has the problem discussed in this thread. Time Machine backups cannot be completed...blah, blah, blah. Sometimes, the TM backup continues and finishes on its own once she starts to use the Mac Mini. Sometimes it doesn't and the solution is to click on "Back up now" in TM. After a couple seconds, the backup completes. I am using two external HDD as her TM Drives connected to a CalDigit Element Thunderbolt 4/USB 4 Hub. After reading through this thread, my conclusion is that there is no consistent, solid solution to this problem yet. True? Because of that, and since the "fix" for my wife's Mac mini is to simply click "Back up now" to finish the backups, I am reluctant to try all the suggested solutions only to have the problem remain. From those of you who have spent far more time on the issue, do you feel this is the most reasonable way for me to address the problem and hope that Apple eventually decides this issue is worth their time to fix? BTW, I also have a 2018 Intel Mac Mini. No problems with TM backups to its two external HDD formatted as APFS (just like the new Mac mini). It is also running MacOS 15.2.

I also have a Mac Mini M4, a MacBook Air, and an M1 mini and Time Machine (Sequaoia 15.2) used to have the problems mentioned in this thread, but I did something suggested in the thread and it fixed it. Unfortuately I can't remember what it was but it was on this thread.

Hi bruiselle, Sadly, just connecting one backup HDD to one of the Thunderbolt 4 ports in the back of the Mini did not solve the problem. So, for me, directly connecting the backup hard drives to the Mini is not a solution. I could switch to Carbon Copy Cloner, but I really don't need its extensive functionality and it seems a shame to pay for a pretty expensive application to solve this problem. CCC is usually set to backup once a day and what I may do is steal that idea and apply it to TM for now. Instead of backing up every hour (not really necessary in my case) I think I will set it to back up "Everyday" and when I am usually on my computer. (I assume it sets the time of the day when it will backup to the time the user initiates the "Everyday" option.) This will hopefully mitigate the annoyance of manually using "Back up Now" because the problem only occurs when the Mini is locked. The good news is I have all the ports on my Mini back. Since there was no difference in performance between direct connection to the Mini and connecting my backup drives to my CalDigit Thunderbolt Element hub, I reconnected the two backup hard drives to the Element hub. Thanks so much for going along with me on this adventure and trying to help.