Time Machine quits backup in OS27

Time Machine can stop backing up even when the LaCie drive has plenty of free space and WhatsApp has been removed. 

The safest next step is to check the LaCie for file-system errors using Disk Utility, without erasing the drive or deleting any existing backups.

Open Applications >> Utilities >> Disk Utility, choose View >> Show All Devices, select the LaCie volume, and click First Aid >> Run. 

If necessary, repeat the check for the other volumes and the physical drive. Apple's instructions are here: Repair a storage device using Disk Utility. 

If First Aid reports errors it cannot repair, stop and protect any important existing backups before proceeding.

If First Aid completes successfully, check the connection between the LaCie and your Mac mini. If you're using USB or Thunderbolt, connect the drive directly to the Mac rather than through a hub or dock. 

If possible, try a different cable or port. An intermittent connection can interrupt a backup even when the drive has plenty of free space.

It's also worth checking the available space on the Mac mini's internal drive. 

Go to Apple menu >> System Settings >> General >> Storage. 

If the internal drive is nearly full, free up some space and try the backup again. Having enough room on the LaCie does not necessarily mean the Mac has enough working space.

Next, reconnect the LaCie, leave the Mac running and logged in, and start a manual backup from System Settings >> General >> Time Machine, if that option is available. 

Pay attention to when it stops. Does it quit during “Preparing backup,” start copying files and then stop, or fail almost immediately? If an error message appears, make a note of its exact wording.

If the problem continues, consider whether third-party antivirus software, disk utilities or other backup applications might be interfering. Check that they are up to date, and temporarily disable relevant software only if necessary and safe to do so.

As a further test, if you have another suitable external drive, try setting it up as a separate Time Machine destination. If that backup works, the LaCie, its connection, its file system or its existing backup may be involved. 

If the second drive fails in the same way, the problem may lie with the Mac or macOS.

I would not erase the LaCie or delete its existing backups just yet. First, make sure anything important is safely preserved.

For Apple's additional troubleshooting steps, see If you can't back up or restore your Mac using Time Machine.

My problem is solved and thanks for your advice. WhatsApp for Pc dugged in deep on my Mac . After removing and cleaning anything with the name WhatsApp,there was still more than 1GB hidden in Containers/Message/Media.

After removing, Time machine made a complete back-up. Greetings from Holland.

Have you rebooted your Mac? If not, that's the first step. If that does not help, then see if the problem is present when you boot in safe mode. That process performs some system cleanup and clears caches, and also disables 3rd party extensions that may cause problems.

Start up your Mac in safe mode - Apple Support

If the above doesn't work, then use the following fix.

Ensure that you have deleted that specific file.

• In Finder, select Go menu > Go to Folder
• Paste the following then press return.

~/Library/Group Containers/group.net.whatsapp.WhatsApp.sha-red/Message/Media/16956631601161@lid/1/b/

• Locate and delete that specific image file, then empty the Trash.
• Run the TM backup again.