I'm having similar difficulties with my strobes firing. Same Inon strobe(s) using fiber optic cables. Nauticam D7000 housing. I'm missing so many shots because of a delay of the strobe(s) firing. I've had very few instances when the strobes fire instantly. By the time the strobes fire my subject has moved or is out of focus.
I've had my gear for four years and I think the delay has increased significantly. Batteries are fresh. I can frame my subject, pull the shutter release and nothing happens for a few seconds. This is extremely frustrating as this equipment is expensive. It should be working. I can't help to think it might be a camera setting. The camera is taking to long to calculate the amount of power the flash needs.
I'm going to call Reef Photo and see if they have any ideas.