Architect Flow 503 Errors Under Load in Singapore Region

Context:
Running JMeter 5.6 tests against Genesys Cloud Architect flows in Singapore. Simulating 200 concurrent voice interactions. The /api/v2/architect/flows endpoint returns 503 Service Unavailable errors when call volume spikes, despite staying within documented WebSocket limits. Using standard HTTP requests for flow validation before routing.

Question:
I cannot figure out why the flow evaluation fails with 503s under moderate load. Are there hidden capacity limits for flow execution in the Singapore region that aren’t documented? How should I structure my load test to avoid hitting these thresholds?