Also tried the 'particle keys doctor ’ with the following output (I replaced my actual device id with ‘my device id’);
particle-cli v1.20.1
! A newer version (1.21.0) of particle-cli is available.
! Upgrade now by running: npm install -g particle-cli
Found DFU device 2b04:d006
Found DFU device 2b04:d006
New Key Created!
Found DFU device 2b04:d006
Found DFU device 2b04:d006
Saved!
spawning dfu-util -d 2b04:d006 -a 1 -i 0 -s 34:leave -D <my device id>_rsa_new.der
dfu-util 0.9
Copyright 2005-2009 Weston Schmidt, Harald Welte and OpenMoko Inc.
Copyright 2010-2016 Tormod Volden and Stefan Schmidt
This program is Free Software and has ABSOLUTELY NO WARRANTY
Please report bugs to http://sourceforge.net/p/dfu-util/tickets/
dfu-util: Invalid DFU suffix signature
dfu-util: A valid DFU suffix will be required in a future dfu-util release!!!
Deducing device DFU version from functional descriptor length
Opening DFU capable USB device...
ID 2b04:d006
Run-time device DFU version 011a
Claiming USB DFU Interface...
Setting Alternate Setting #1 ...
Determining device status: state = dfuIDLE, status = 0
dfuIDLE, continuing
DFU mode device DFU version 011a
Device returned transfer size 4096
DfuSe interface name: "DCT Flash "
Downloading to address = 0x00000022, size = 609
Download [=========================] 100% 609 bytes
Download done.
File downloaded successfully
Saved!
attempting to add a new public key for device 3c0021001547353236343033
submitting public key succeeded!
Okay! New keys in place, your device should restart.
The device rebooted with the same result - sitting flashing cyan with an occasional slower orange flash twice.