Lost all my Zigbee devices in Z2M after updates

After a few updates the other week, I have lost all my devices from Zigbee2MQTT and so far I've been unable to recover them..

My setup:
HAOS 2026.6.0 running on an HP Prodesk
SLZB-06P7 on PoE - firmware 3.3.1
Zigebee2MQTT - v2.11.0-1

What happened:
After a flurry of updates, I spotted that Z2M was not starting. Checking the logs, I could see this error:
Error: network commissioning timed out - most likely network with the same panId or extendedPanId already exists nearby
I was wondering why this is in the logs, as nothing in the configuration had been changed and I only have one zigbee network. The zigbee network itself appears to be working, remotes paired to devices still operate things, so I can turn some lights and a fan on and off still.

What I have tried:
I tried hard reboots of both HA and the SLZB, still getting the same error. Remembering some updates had applied, I tried to remember what. I recalled HA Core ans Z2M itself had updated, so I reverted both to previous backups. After that, Z2m would now start up, but all devices had vanished from it. Checking the Z2M configuration.yaml showed all the devices still there (well, all but the 4 most recent additions, I think my backup was a bit older).

Then I came across this thread:

So I checked my SLZB firmware and sure enough, I was on a DEV version! So next thing was to roll back the firmware, that done, still no change in the zigbee devices. I even tried the "take aerial off and refit" trick to no avail.

So where I'm at now, there are no zigbee devices showing. Configuration.yaml shows devices. coordinator_backup.josn does NOT show anything listed under devices. MQTT itself still shows the devices listed, but unavailable. If I load the network map in Z2M, it is recognising the coordinator and showing it has 10 siblings but all of those siblings are showing unknown.

Any guidance to what I should look at/try next would be gratefully appreciated.

Hi, all I can add: I have no experience with LAN coordinators but with USB versions, taking them down (power cut) can help with certain issues.

Have you tried deleting the backup file?

A screenshot of your Z2M error log would really help...

Hi Nick, thanks for responding, I've tried power cycles on the coordinator several times during the debug process, no luck.

Hi LC, it's in Debug mode at the moment so quite verbose, is that what you need or should I set it to anther mode first?

Which backup file are you referring to to delete?

After much fudging around, I have 8 devices back online, 2 devices failing LQI (thus offline but showing, the other 10 devices are still MIA. This was achieved by replacing the contents of the database.db file with that of a very old back up. I'm still missing the other 10+ devices however.

Some things I have read implied that the SLZB should still contain a list of devices that could be re-read back in to Z2M, but following the instructions has resulted in nada. Along with finding the follow article on the SMLight site, I am getting resigned to the fact I will probably have to start from scratch again.

https://support-legacy.smlight.tech/supportcenter/public/en/blog/empty_dev_list_ota