Having completed the update on my RPi2, I decided to perform the update on one of my TBS2910 boxes.
I placed the LibreELEC-imx6.arm-7.0.2.tar file in the update folder, over a samba connection, and then rebooted.
After viewing a blank TV screen for a minute, I ssh'd in to the system - this confirmed that LE was definitely running since the old OE password no longer worked!
I discovered that Kodi was repeatedly crashing and restarting.
I renamed my old .kodi folder so that the system would be in 'virgin' state, and rebooted, which resulted in exactly the same symptoms!
My full logs are here: logfiles
I would be grateful for advice on how to recover the system.