New MI8 lag and at reboot Lost ALL data

[Calligari]

two time with 2 different rom, 8.9.1 and last jully version.
system lag, error message 'xx not respond''. and on reboot nothing on the phone !
data is empty, no backup, nothing in data.
and the locked /persist partition make difficult a new installation of system. (i make a tutorial for overwrite this lock)

you have a idea of the source of my problem?

 

[humrum]

Yes, I had something like this too. System lags, becomes unresponsive and won't restart...
Already formatted the ohone 4 times