[oe] Build looping with "Checking sstate mirror object availability...done"?

[Alex Kiernan]

Our local master jenkins build looks like it's started looping with:

00:56:28.368  Checking sstate mirror object availability...done.
00:56:28.368  Checking sstate mirror object availability...done.
00:56:28.368  Checking sstate mirror object availability...done.
00:56:28.752  Checking sstate mirror object availability...done.
00:56:28.752  Checking sstate mirror object availability...done.
00:56:29.136  Checking sstate mirror object availability...done.
00:56:29.136  Checking sstate mirror object availability...done.
00:56:29.136  Checking sstate mirror object availability...done.
00:56:29.520  Checking sstate mirror object availability...done.
00:56:29.520  Checking sstate mirror object availability...done.
00:56:29.904  Checking sstate mirror object availability...done.
00:56:29.904  Checking sstate mirror object availability...done.
00:56:29.904  Checking sstate mirror object availability...done.
00:56:30.288  Checking sstate mirror object availability...done.
00:56:30.288  Checking sstate mirror object availability...done.

The only changes from it's previous build are these two:

Layers Update: poky
* poky 9d606cf...f48ef0b (2):
 > build-appliance-image: Update to master head revision
 > sstate: Ensure SSTATE_PKG is reloaded when handling siginfo

Its sstate-cache is on NFS (well AWS EFS) if that's relevant?

At the point I killed it, it was just over an hour in, but was only a
100 tasks into the 7392 - a full rebuild is normally ~3.5 hours, but
this didn't seem to really be making any meaningful progress.

-- 
Alex Kiernan