Mojave won't delete my empty directory

I have a directory which is definitely definitely empty, but Mojave says it isn't, and won't delete it.

Last week my MBP died. On Monday my new 2TB iMac 5K arrived, I put the MBP disk in a USB3 enclosure and used Migration Assistant to transfer the data (after it had updated the iMac to the latest High Sierra to match the MBP). All seemed well, and finished just as Mojave became available, so I updated the iMac to Mojave 10.14.

Whilst tidying up the next day, deleting a Lightroom 'Previews.lrcat' tree (for what that's worth), it failed to delete a directory named "C8E6".

Finder said the item was in use (which I doubted, and anyway lsof didn't find anything);

"rmdir" said "Directory not empty"; "rm -rf" said the same.

There doesn't seem to be anything in there:

$ ls -Rail C8E6/

total 0

786499 drwxr-xr-x 3 me staff 96 20 Jan 2016 .

12886106817 drwxrwxrwt 3 root wheel 96 28 Sep 19:19 ..

Contrast with this, which does seem to think it's empty:

$ rm -ri C8E6

examine files in directory C8E6? y

remove C8E6? y

rm: C8E6: Directory not empty

That link count of 3 on "." - which should be 2 on an empty directory - suggests either a subdirectory or corruption, and as you can see we're all outta subdirectories.

I know Time Machine makes hard links to directories, but I don't know how to investigate that.

I did a Disk Utility "First Aid", which was happy, and rebooted single user and did an fsck, which was also happy, remounted rw and tried to delete, but it wouldn't. I rebooted in safe mode too, for completeness, but I was still unable to delete.

I've moved the directory to Trash (which worked) and tried to empty it (which didn't); I tried the "really really empty Trash" meta-key combination, but that made no difference.

In case Apple were doing something clever with "ls" & "rmdir", I even made a C program to do opendir/readdir & rmdir, but they behaved as expected (i.e., showed only "." and "..", and failed to rmdir with errno 66 "Directory not empty".

Any suggestions?

The link count bothers me, not least because it doesn't seem to bother fsck.