Thanks for the reply, but no progress.

My steps are:

Core2 device connected
Core2 device = Private (on display)
logged in to the UI2flow. It shows Core2 as Public, red

• Core2 unregistered in UI2flow
• Core2 not visible in UI2flow
• registered to M5Burner, downloaded last FW 2.3.0-Core2
• Press Burn, Erase → Erased successfully
• Press Burn, Start, Baud Rate default (1500000)
• Checking device...
• Burn UIFlow2 pop-up window froze
• Waited 2 min.
• UI2Flow page refreshed
• Waited 30 min. → no change
• Closed Burn pop-up window
• Reopened Burn pop-up window
• Press Burn, Erase → Erased successfully
• Set BaudRate to750000
• Erased successfully
• Checking device...
• Waring: ...bind your account now? → Yes
• Binding device → keep settings to "Public" → next
• Binding device successfully
• Press Erase
• Erased successfully
• Brun, Set BaudRate to750000
• Checking device....
• Configure, filled Wifi credentials → Next
• Burning
• Core2 restarted, Burn successfully
• I can see on display "Private" again
• Core2 is visible in UI2Flow as Public, red. (After reloading the page).

Any idea?
Thanks