Custom Engine Agent latency 5-7 seconds before webhook is called

We have a Teams bot that we recently extended with Microsoft 365 Copilot support using the copilotAgents.customEngineAgents manifest configuration.

When users send messages to our agent through the Copilot sidebar, there's a consistent 5-7 second delay between when the user sends the message and when our Bot Framework webhook receives the activity.

Some extra notes:

• When users message the same bot directly in Teams (not through Copilot), messages arrive immediately with no delay
• When we send messages from our backend to Copilot (using the serviceUrl for proactive messaging), they arrive immediately with no delay

So the latency only occurs in one direction: Copilot → our webhook.

Manifest Configuration:

{
  "$schema": "https://developer.microsoft.com/en-us/json-schemas/teams/v1.17/MicrosoftTeams.schema.json",
  "manifestVersion": "1.21",
  "version": "1.1.1",
  "bots": [
    {
      "botId": "<client_id>",
      "scopes": ["personal", "team", "groupChat"],
      "isNotificationOnly": false,
      "supportsCalling": false,
      "supportsVideo": false
    }
  ],
  "copilotAgents": {
    "customEngineAgents": [
      {
        "type": "bot",
        "id": "<client_id>"
      }
    ]
  }
}

Environment:

• Azure Bot Service (not Copilot Studio)
• Bot region: Global
• Messaging endpoint hosted in AWS us-east-1

Questions:

1. Is this delay expected behavior for Custom Engine Agents?
2. Is there any configuration to reduce this latency?
3. Are there plans to optimize Custom Engine Agent message routing?

This latency significantly impacts user experience - users expect near-instant responses when chatting with an agent.