Safecom SAMR-4110

Does anyone know if this device is particularly susceptible to supply
brownouts?

i.e. when the mains supply voltage dips to say 50% of its nominal value
for say half a second.

I have one in an unattended installation that locks up around once a
week due to brownout events. I have verified that this is the cause
with a Variac (voltage variable transformer).

The Ready light (normally flashing) stays on or off continuously and you
cannot talk to the device through the LAN port.

TIA