This is a new setup, S900 with GH3, after its powered up there is an image on FPV, after the shutter releases, there is nothing on FPV, but shutter works fine when toggled. Any help would be great..!

I am not expert on GH3 so take with a grain of salt.
But if you have an image on the FPV that means all is working from output of camera to the FPV transmitter and then to ground.
So my suspicion would be the video out of the GH3 is being shut off by the shutter command or is outputting a incompatible output.
Do you have the latest GCU firmware there was some video out problems resolved by 2.2 FW I think.
Also check your camera setup :
Mode as Creative video
MF/AFC/AFS/AFF Select: Select AFC.