Cannot finish first backup with Time Machine My first Time Machine backup systematically fails when it is about to finish.

I looked at the system logs and I have these errors:

Failed to unmount '/Volumes/Copies de sauvegarde Time Machine' (disk2s2), dissenter: {
    DAProcessID = 263;
    DAStatus = 49168;
} with status: 49168 (null)

Failed to eject 'disk2' using DiskArb, dissenter: {
    DAStatus = 49168;
} with status: 49168 (null)

Failed to eject 'disk2' (using ioctl), error: 16 Resource busy

Failed to remove directory '/Volumes/com.apple.TimeMachine.TimeMachineFolder-28BD73CD-4059-43D4-B1BE-0CA9C98D5EFD', error: 16 Resource busy


I have macOS 10.14.6 (18G103)

Any idea of the problem?
Anecdotally, after having seen similar several times, two things to try; one free, the other paid.

First clear down any stray local backups, from Terminal.

tmutil listlocalsnapshots / will list them.
tmutil thinlocalsnapshots / 1000000000000 1 will pretty aggressively cull them.

List again afterwards &amp; make sure only one or two remain, &amp; that none of them are tagged dataless.

Try running Time Machine again.

If still no joy, then the only way I've ever found to fix this is to run DiskWarrior on the Time Machine drive. Apple's Disk Utility never seems to work.
Fortunately, TM drives must be HFS+, as Disk Warrior cannot yet handle APFS.