Dead unit, when firmware upgrade

This happened to me two times, on the exact place.

ePMP 1000 connectorized configured STA mode.

upgrade firmware, ERROR.

the unit become unnressponsive but passes traffic.

GUI not available

SSH available, I select reboot, but it answer "killed".

after some minutes, the units dies completely.

It happened two times on two different units in the exact place. UPS everything correct.

what can I do ?