Predictive Routing 503 errors during JMeter load test

Trying to understand why predictive routing drops calls at scale. Running JMeter 5.6.2 from Singapore to simulate 300 concurrent inbound calls hitting a predictive outbound campaign.

  • Genesys Cloud Org: Sandbox
  • JMeter Threads: 300
  • Ramp-up: Instant

The first 100 calls connect fine. After that, we get 503 Service Unavailable errors on the WebSocket handshake. Is this a hard limit on predictive routing capacity or a config issue?