Time machine backup failing

Hi there,

I have a MacMini which has been backing up previously but for some reason at some stage the backups have started failing. I'm on my 3rd External Drive and it's happening with all of them (the current one is brand new). The MacMini is less than 2 months old and I have very little stored on it.

The error message I get is 'An error occurred while copying files. The problem may be temporary. If the problem persists use Disk Utility to repair your backup disk.'.

I'm running Mojave (10.14.1) on a Mac mini (late 2014 model) with a 288Hz i5 and 8GB 1600MHz DDR3. I'm not an expert but I've tried looking for the error in console and see quite a few messages but I don't really understand what they mean. There are a few of these that just keeps repeating during the backup process is:

Nov 16 12:04:32 Toms-Mac-mini com.apple.xpc.launchd[1] (com.apple.mdworker.shared.09000000-0000-0000-0000-000000000000): Service only ran for 7 seconds. Pushing respawn out by 3 seconds.

Nov 16 12:04:33 Toms-Mac-mini com.apple.xpc.launchd[1] (com.apple.mdworker.shared.

and this one:

Nov 16 12:06:29 Toms-Mac-mini com.apple.xpc.launchd[1] (com.apple.imfoundation.IMRemoteURLConnectionAgent): Unknown key for integer: _DirtyJetsamMemoryLimit

Nov 16 12:13:46 Toms-Mac-mini FollowUpUI[2420]: DEPRECATED USE in libdispatch client: dispatch source activated with no event handler set; set a breakpoint on _dispatch_bug_deprecated to debug

There are obviously loads of others but these seem to be quire frequently reoccurring.

I've tried backing up to new drives, I've uninstalled Norton which was the only thing I could think of that may have been messing things up but still no luck.

Is anyone able to help?

Many thanks,

Tom