Mojave disk partitioning errors

I've been fighting with Bootcamp for a while now on my late-2014 Retina iMac.

I've just upgraded to Mojave (10.14.2) to see if it solved any issues. It seemed to fix some but has introduced another problem with partitioning the drive. Basically, when I try to partition the drive in Bootcamp I get the following error.

I go in to Disk Utility and run a first aid and get an error with the fsroot tree which doesn't seem to be fixable:

Running First Aid on “Macintosh HD” (disk2s1)

NOTE: First Aid will temporarily lock the startup volume.

Verifying file system.

Volume could not be unmounted.

Using live mode.

Performing fsck_apfs -n -l -x /dev/rdisk2s1

Checking the container superblock.

Checking the fusion superblock.

Checking the EFI jumpstart record.

Checking the space manager.

Checking the space manager free queue trees.

Checking the object map.

Checking the Fusion data structures.

Checking volume.

Checking the APFS volume superblock.

The volume Macintosh HD was formatted by hfs_convert (945.230.6) and last modified by apfs_kext (945.230.6).

Checking the object map.

Checking the snapshot metadata tree.

Checking the snapshot metadata.

Checking the extent ref tree.

Checking the fsroot tree.

error: inode_val: object (oid 0xc0044): invalid parent_id (0x0)

fsroot tree is invalid.

The volume /dev/rdisk2s1 could not be verified completely.

File system check exit code is 0.

Restoring the original state found as mounted.

Operation successful.

So, I then booted in to Recovery mode and tried again, same error. Now I'm stuck at what to do next.

Appreciate any pointers!