Problem plugging surge protected power strip into gfci outlet?
If either the power strips or connected equipment have capacitors between the power conductors and ground, there would be some current to ground through the capacitors. If there are MOVs between power and ground, there could also be some leakage through those. Deterioration of insulation can also result in small intermittent leakage currents to ground before the insulation actually fails and trips the GFI or breaker every time the faulty device is plugged in.