WC1 401 error after consecutive create case & screen_async requests

I have about ~1000 organizations I am trying to load into the WC1 pilot environment.
Doing some throughput testing and I'm getting getting consistent 401 errors after creating a case and performing the async screening request after ~10-15 requests. On an immediate restart, works fine (continuing from the organization it failed on) and returns 401 again after successfully creating another ~10-15 requests. Each SEQ_case_create_organization and SEQ_screen_async are separated by a 2 second delay.