Clone (rsync) of 10.14 startup drive fails to boot

Config:

Stock MacBookPro10,1

10.14b11 (18A389)

Terminal added to Full Disk Access

Cloning an APFS FileVault startup volume to a USB3 HDD HFS+J external volume (formatted using DiskUtility) fails to boot. The verbose log has entries like:

"Warning: kextd unavailable"

"com.apple.xpc.launchd[1] <Error> rootless-init: signaled: Segmentation fault: 11"

...

"com.apple.xpc.launchd[1] (com.apple.xpc.launchd.domain.system) <Critical> No task-access server configured! The system will not get very far."

... more setup and then eventually it gets into this infinite loop of:

"AppleKeyStore: operation failed (pid: 241 sel: 7 ret: e00002c2 '-536878286' -100000)"

...Where this pid is incrementing by 1 forever. It will also print a block of:

"Can't get kextd port."

... And then loop into the AppleKeyStore messages again

I have not tried APFS->APFS (generally because APFS is slow and tends to get corrupted on HDDs), nor have I tried HFS->HFS.

But, APFS->HFS worked (and still works) in 10.13.x.

My clone procedure is:

- Format external drive as HFS+J, then

sudo diskutil enableOwnership disk2s2
sudo rsync -xrlptgoEvHS --progress --delete / /Volumes/Clone
sudo bless --folder /Volumes/Clone/System/Startup/CoreServices --bootefi

I then option-boot to the disk picker and select the Clone drive.

Diskutil layout:

$ diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *251.0 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                 Apple_APFS Container disk1         250.1 GB   disk0s2
   3:       Apple_KernelCoreDump                         655.4 MB   disk0s3


/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +250.1 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume Macintosh HD            148.1 GB   disk1s1
   2:                APFS Volume Preboot                 53.4 MB    disk1s2
   3:                APFS Volume Recovery                512.1 MB   disk1s3
   4:                APFS Volume VM                      1.1 GB     disk1s4
   5:                APFS Volume CloneTest               2.3 MB     disk1s5


/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                  Apple_HFS Clone                   999.9 GB   disk2s2

rsync did print a few "operation not permitted" warnings but they were all for folders that were restricted in 10.13 too (generally in "/var/folders/bs/<uuid>/0").

Any ideas on how to fix this?