Beckoff modules blackout at "other slaves" startup

I don't know exactly what happen inside linuxcnc but I'm having this issue :  Ethercat issue video
at LCNC startup I power on the servos via a relay and the the whole Beckhoff modules blackout in LCNC but stays on physically, the lights don't even flash. 
This causes the first and second servos (sometimes the third) to not be set as operative.
If you want to try out yours I had to setup on HAL this to turn on halshow at startup: loadusr halshow
Any guess?

I have a solid state relay OMRON G3PE 525B, for what I know it will not need flywheels

I forgot to mention this happen only if the first slave is connected (EK1100 --> First slave --> second slave --> etc... )
if EK1100 --> disconnect --> second slave --> etc... it doesn't blackout.

so my guess is that it's not an electrical or EMI issue, but something software side

You should have the servo drives switched on when you start linuxcnc.
That way linuxcnc can make them go up and down as required, and change cia402 states as required.
There is an "enable" pdo you connect to joint.amp-power-on or something like that, to enable the drive.

I think what's happening when you switch on the drives is the ethercat master spots new things on the net and
scans the bus and does some setup things for the new devices. This interrupts the cyclic operation
and I would think all slaves exits op mode for a second or two, until ethercat master is ready and the slaves
can be brought up again.

So, don't switch on and off power of the drives while active in linuxcnc.