Shelly devices changing mac addresses on their own

Hi,

I have been running 15+ Shelly devices since about 6 months now and one issue I have been seeing multiple times now is that the devices change their mac addresses own their own. This of course messes with any DHCP reservations and leads for sure to newly assigned IPs which will cause all sorts of issues with any automation in place. A few more things which I have narrowed the problem down to:

1. The change of mac addresses seems to be connected to these devices reconnecting to the WIFI access point (e.g. after restarting the router)
   1. In my set up I have multiple wifi access points (same SSID), so there is always at least one up and running to connect to even if the other is down
2. If it happens it always happens to all Shelly devices of the same type, examples: all Shelly Plugs (example attached), next time all Shelly Vintage Bulbs, next time all Shelly H&Ts and so on.
3. Seen this on various firmware versions for each device
4. It is always the first 6 digits of the mac address which change, the second half seems to be static and mapped to the device name (again, see attached screenshot for examples
   1. The first 6 digits seem to be based on the access point and are consistent across all devices?

I have not found a pattern to this yet and can also not reproduce it at will by just rebooting an access point. There is no consistent frequency to this either: Sometimes it does not happen for months even with weekly access point reboots,

My expectation would be for a mac address to never ever change on its own on any network device, but apparently that's not the case which violates very basic networking best practices, or am I missing something here? Any pointers or ideas welcome.

Thanks!

I am not aware of the mentioned short/long ID feature and also I am unable to find it anywhere in the settings menu. Where do you set this exactly and what does this do?