No luck I’m afraid. The full reset went through fine and I got the bridge back online (with no devices), but when I chose to do the firmware update to the latest beta I got the same error, which I now realise I forgot to mention was a communication issue (error 108).
I’ll do the reset again and reload my last backup. Note to self, no need to rush around in a blind panic trying to find the backup files, they are available in the app on my phone, even if the bridge has been reset 
Will post in the backups topic from a few years ago to check on the location of the files.
Not sure how much help I can be for the next few days… might be next week before I can look at it again if you want to try and troubleshoot it further.