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A2A connected agent: "Error code: SystemError" on retry after first-time auth

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Posted on by KM-29060643-0

Summary

We have an external agent connected to a Copilot Studio agent over the Agent2Agent (A2A) protocol (Authentication = OAuth 2.0). The connection is created and validated successfully, but the conversation fails with a generic "Error code: SystemError" specifically when the user clicks Retry after completing the first-time connection sign-in. Starting a brand-new chat session with the same agent works correctly.

Environment / setup
- Copilot Studio agent with a connected A2A agent (Authentication = OAuth 2.0).
- Reproduced in the Test canvas (channelId: pva-studio) and the published M365 Copilot channel (channelId: m365copilot).
- Our A2A endpoint implements the A2A 1.0 spec (message/send returns a Task; clients poll tasks/get).

Symptom
User sees: "Sorry, something went wrong. Error code: SystemError. Conversation ID: <guid>. Time (UTC): ..."

Steps to reproduce
1. Start a new chat and send a message that invokes the connected A2A agent.
2. Copilot shows: "Let's get you connected first... Open connection manager to verify your credentials. Once the connection is ready, retry your request." with a Retry button.
3. Complete the connection sign-in, then click Retry.
4. -> SystemError.
5. Starting a brand-new session (instead of clicking Retry) works correctly.

What we've verified on our (the A2A agent) side
- Every request we receive returns HTTP 200 with a valid A2A Task payload; no exceptions or 5xx on our server.
- At the moment the SystemError is shown on Retry, we see no corresponding request reaching our server.

Questions
1. Why does Retry after a first-time connection sign-in produce SystemError while a fresh session succeeds?
2. Is there a known issue with the just-established connection token not being attached on the Retry request?

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Categories:

Copilot Studio pre-built agents/templates

Autonomous agents

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Ashlesha-MSFT Microsoft Employee on at

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Thanks for the detailed report, this is very helpful.

Based on your observations, this looks like a Retry-path issue in Copilot Studio/A2A orchestration rather than an endpoint failure on your side:

1. New session works with the same connection and same agent.
2. Retry after first-time OAuth sign-in fails.
3. No request reaches your A2A service when Retry fails.

That pattern usually means the failure happens before outbound dispatch, possibly in connection state refresh or token/context rehydration for the Retry action.

Answers to your questions:
1. Why Retry fails but fresh session works:
Likely Retry is using stale or not-yet-propagated connection context after first-time auth, while a new session rebuilds context correctly.
2. Known issue with token not attached on Retry:
Your symptoms are consistent with that class of issue. Even if not publicly documented yet, this is valid for engineering investigation.

Recommended next steps:
1. Repro once in a minimal clean tenant/agent setup to confirm consistency.
2. Open a Microsoft support ticket as a probable product bug.
3. Include Conversation ID, UTC timestamp, channel, tenant ID, and a HAR/network trace.
4. Attach evidence that no outbound request hit your A2A endpoint during failed Retry.
5. Include one successful fresh-session trace right after the failed Retry for comparison.

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Sayali-MSFT Microsoft Employee on at

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Hello KM-29060643-0,

We will proceed with raising this as a bug from our end. Based on our analysis, the failure occurs specifically when using the Retry option after completing the first-time OAuth sign-in. No request is reaching the A2A agent during this step, while starting a new chat works as expected. This indicates the issue is likely within Copilot Studio (session/connection context handling) rather than the external A2A service.

As a temporary workaround, please start a new chat session after completing the connection instead of using the Retry button.
can you share the capture the Conversation ID, UTC timestamp, channel (pva-studio / m365copilot), affected user, and confirm that no backend request reached the A2A endpoint during Retry.

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11manish 3,333 on at

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Everything you've validated points to the problem occurring inside Copilot Studio, not within your A2A implementation. Because no request reaches your endpoint during the failing Retry operation, it's unlikely that the issue is related to the A2A 1.0 protocol or your OAuth implementation. The most probable cause is that the existing conversation doesn't refresh its authentication context after the first-time OAuth sign-in, whereas a new conversation does.

I recommend opening a Microsoft Support ticket and providing:

The Conversation ID

Correlation ID (if available)

UTC timestamp of the failure

Confirmation that no request reaches the A2A endpoint on Retry

Confirmation that starting a new conversation succeeds immediately using the same connection

This evidence will help Microsoft determine whether the Retry mechanism is failing to refresh or attach the newly established OAuth connection before invoking the connected A2A agent.

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