Backups work but then they fail after a while

[Tonicherif]

I installed the most recent beta of the app and had first issues to start Time Machine with my login credentials. But then it worked after removing the drives from the TimeMachine settings. And restarting my Mac. Now the backups start but after a while of data backup, the backup fails and I get an notification.
The TM backup start again... With the same result after a while.

[jamesyc]

What is the error? Can you give me the logs?

https://github.com/jamesyc/TimeCapsuleSMB/blob/main/FAQ.md#how-do-i-get-logs-from-my-mac

[Tonicherif]

Hi James, thanks for the fast reaction. There is no special error, it shows only "backup failed ..." (in German "Backup fehlgeschlagen ...") in the menu. See attached screenshot with installed macOS 26.5.1. I have this issue on two machines (MBP M1 and Mac mini M4)

and here is the log:
tm-live.log.zip

btw. in you FAQ you should also mention to "mkdir -p /tmp/tm-debug" before running the log command. Otherwise you get an error that the directory does not exist.

[jamesyc]

Log window is only 2026-06-03 11:32:34 to 11:35:36.

No real backup markers: no backupd-helper, diskimagesiod, NetAuthSysAgent, SMB session, sparsebundle/backupbundle attach, mount, copy phase, or failure line.

So you captured logs after the failure, or didn’t start logging before reproducing the failure. We need a new capture where you start log stream, then start the backup, then let it fail.

[Tonicherif]

Hi James, sorry my fault that the log didnt capture the issue. Please see attached a new log hope now you can see whats going on. Thanks a lot!_

tm-live.log.zip

_

[jamesyc]

This log only spans 2026-06-04 21:28:03 to 21:28:43.

It contains 80 smb_iod_start_reconnect kernel entries, repeating every ~2s from 21:28:05.428 through 21:28:43.459.

It does not include the actual Time Machine failure line, backup copy phase, disk image attach/detach, or a disk disappearance/unmount event.

[Tonicherif]

Thank you. I generated the log immediately after the backup failed.
Is there anything else I can do that might help you gather more information about the issue?
In the meantime, I'm going to try installing version 2.1.8 and see whether the problem still occurs with that version.

[Tonicherif]

One additional detail that may be relevant:

The backup itself appears to complete successfully and the data is copied to the Time Capsule. The error only occurs right at the end of the process, during what seems to be the finalization or cleanup phase.

Instead of reporting a successful backup, macOS then displays a message saying that the backup failed.

Perhaps this helps narrow down where the problem occurs.

[jamesyc]

That logging command only captures events when it is running. If you run it for 30 seconds after the backup already failed, then it cannot log anything. You'd need to leave the log running.

This will take up a lot of space, so you might want to trim off the non-relevant parts of the log before uploading. So if the backup fails at 9:00am, delete the parts of the log before 8:50am and after 9:10am.