Mitsubishi VRF - long delay for indoor EXV opening

Dear All,
I have a system Mitsubishi inverter model PUHY-P900YSJM installed with 18 indoor units
the system is working fine while electrical power is steady.
The system is installed in a region where we have sudden power failures and customer move to generator system.

After each power failure, the unit is not running properly.
one compressor is running on 20Hz steady for around 15-20minutes, the suction pressure is very low and the unit is shutting down on low pressure.
the units returns to normal operation after 25-30minutes after resume of power on the unit.

after carefully checking the system, we noticed that after each power failure, their is no COMMAND to the indoor expansion valves to open which is causing the low pressure. The command is only sent after 25-30minutes after power is resumed to the unit.

is this a programmable setting, how can we program it?
or what can we do?

thanks,

You cant do nothing/ May be UPS for PowerBoard)))

thanks for the reply
when we connect only the power board to a UPS, and we face a power failure, will it not signal an alarm due to loss in power in the compressor and indoor thermostats?
is it automatic reset or needs manual reset?