Time Machine stops after a few gigabytes, without any visible error message I had to reinstall macOS recently, and ever since, I am not able to back up. After a Prepare phase, it gets to backing up some 5-6 Gigabytes (if I am lucky), then it stops ("Stopping..." as seen in preferences). It was working perfectly before.


I am using High Sierra 10.13.3.
I am on APFS
I am trying to backup to a Time Capsule (firmware version 7.6.9) over wi-fi
I am using a MacBook Air from 2012
I have tried restarting Time Capsule (which triggers an fsck)
I have tried to reuse same backup as before, or create an entirely new backup
I am trying to use an encrypted backup (backing up without encryption is not an option for me)
I have tried excluding system folders from backup so that only /Users remains


As I said, there are no visible errors. In the system log I see some messages, although I am not sure what to do with them (there is no problem reading mentioned file, and I am not sure why it wants to copy to (null), maybe it has lost connection or something, but the situation is not clear).

Error: (-36) SrcErr:YES Copying /Volumes/com.apple.TimeMachine.localsnapshots/Backups.backupdb/R'lyeh/2018-02-08-110642/R'lyeh/Users/zsszatmari/projects/servehome/node_modules/babel-preset-es2015/node_modules/babel-plugin-transform-es2015-classes/node_modules/babel-template/node_modules/lodash/function/rearg.js to (null)
Failed to unmount disk mounted at '/Volumes/com.apple.TimeMachine.localsnapshots/Backups.backupdb/R'lyeh/2018-02-08-094426/R'lyeh', error: {
    Action = Unmount;
    Target = "file:///Volumes/com.apple.TimeMachine.localsnapshots/Backups.backupdb/R'lyeh/2018-02-08-094426/R'lyeh";
}
Failed to delete APFS snapshot with name 'com.apple.TimeMachine.2018-02-08-094426' on volume '/', error: Error Domain=NSPOSIXErrorDomain Code=2 "No such file or directory"


Also:

$ log show --predicate 'subsystem == "com.apple.TimeMachine"' --info | grep 'Backup failed'
2018-02-07 09:45:49.644125+0100 0x8da43    Error       0x41fd0              10549  14   backupd: (TimeMachine) [com.apple.TimeMachine:TMLogError] Backup failed because a backup source disk was ejected or disconnected unexpectedly!
2018-02-07 09:45:49.678109+0100 0x8da43    Error       0x41fd0              10549  14   backupd: (TimeMachine) [com.apple.TimeMachine:TMLogError] Backup failed with error 37: 37
2018-02-07 10:01:14.923986+0100 0x95f8f    Error       0x450cc              11759  14   backupd: (TimeMachine) [com.apple.TimeMachine:TMLogError] Backup failed with error 50: 50
2018-02-07 10:37:38.571642+0100 0xa06e0    Error       0x0                  12807  14   backupd: (TimeMachine) [com.apple.TimeMachine:TMLogError] Backup failed with error 19: The backup disk could not be resolved, or there was a problem mounting it.
2018-02-07 13:26:23.305069+0100 0xa5320    Error       0x0                  13003  14   backupd: (TimeMachine) [com.apple.TimeMachine:TMLogError] Backup failed with error 18: The backup disk could not be found.


I am not sure why would it think that the backup source (the boot drive) is ejected, or why would there be a problem mounting the backup drive.

Thank You.
Problem seems to be solved, I am not sure how.


I deleted the erroneus file, but I don't see why it would cause problem in the first place
By a friend's suggestion I've moved physically closer to the Time Capsule, maybe it is getting older and the wifi connection is weaker
I've deleted a volume from boot APFS container (but it wasn't mounted anyway)


I am still somewhat puzzled, but maybe someone coming by with same symptoms can make use of any of these.