High Bandwidth, High Voltage differential amplifier problems
Surely C4 is in the wrong place: -



It should be across the feedback network and not from -Vin to ground if you want to maintain a balanced amplifier. 

I don't see the reason to have C3 and C4 at all. Just putting C4 where it is does not balance the gain to keep it differential - it does nothing except boost the +Vin gain at high frequencies. The AD8618 input capacitance is about 3 pF and 220 pF capacitors are dwarfing that capacitance. You are bound to get problems with them.