Parabola can import 300k records but will definitely take longer to do so. Is the step stuck calculating or is there no data being returned?
Steps should stop calculating after 1 hour, so there’s a chance this step has stalled or timed out. This can usually be resolved by making another import request.
Are you comfortable sharing a link to your flow or your flow name? Feel free to send it to help@parabola.io and we can further investigate.