I have a smart watch (Zeblaze Blitz) that changes the MAC address when it is rebooted.
Every device I have had has a static MAC address but after rebooting if WiFi is off it just says “Unavailable” under “Wi-Fi MAC Address” then I turn WiFi on and it gets a different MAC address than it had last time, however only the last group of 3 hex (6 characters) change.
It’s annoying as I use MAC Filter/Control on router, so if I reboot the watch I have to put in the new MAC address.
I contacted the manufacturer and they said
"For the MAC address, I confirm for you that it will change all the time as your wifi will also change , like the IP address change, because the MAC address is gotten Automatically, no one can change it, and it also match the wifi Automatically, so we here can use the wifi normally even the MAC address change."