I doubt it would be cutting spark at 0.55bar, I would suggest looking at your coil packs, or possibly spark plugs (has this started since they changed your plugs ?) plug gap ? I had similar thing, changed plugs, all fine.
Does it still cut out with all boost OFF, ie ~0.45bar ? also, post this where the skyline boys can read it in maintenance etc, they might have some more ideas...but I wouldnt be trying FCD.