With 'system.dynType = FixedInitial' an inrush is observed at initial time. Fast dynamics are resolved after switching.
See for example:
meter.p[1] active power in pu, changing from 0.5 (1000 MW) to 0.25 (500 MW) meter.p[2] reactive power in pu, from 0.25 (500 MW) to 0.125 (250 MW)and other meter-signals.