Architect flow timeout on high concurrency load test

Can anyone clarify why Architect flows fail under load?

Background

Running JMeter 5.6.2 against Genesys Cloud 2024.1. Targeting 300 concurrent WebSocket sessions. Basic IVR flow with single menu prompt.

Issue

Requests fail with 504 Gateway Timeout after 15 seconds. This happens when thread count exceeds 100. Flow works fine at low volume.

Troubleshooting

Checked API rate limits. No 429 errors. WebSocket connections stay open. Timeout only occurs on flow execution.