Copilot Studio agent suddenly stopped working in Teams

Hello,

I've run into a strange issue with a Copilot Studio agent and I'm trying to understand where to investigate next.

The agent is published to the "Teams and Microsoft 365 Copilot" channel and was working normally in Microsoft Teams until recently.

• The agent still works correctly in Copilot Studio.
• The agent still works correctly in Microsoft 365 Copilot / Copilot Chat.
• The issue only occurs in Microsoft Teams.

What happens in Teams:

• Messages can be sent to the agent.
• No error message is displayed.
• No response is returned.
• Most importantly, no session is created in Copilot Studio (Analytics / Observability).

Because no session is created, it looks like the message never reaches the agent runtime.

What I've already checked:

• Republished the agent.
• Reinstalled the Teams app.
• Verified the Teams and Microsoft 365 Copilot channel configuration.
• Checked permissions and sharing settings.
• Checked Teams Admin Center configuration.
• Tested in both Teams Desktop and Teams Web.
• Reviewed Microsoft 365 service health.

This same tenant has another Copilot Studio agent that works normally in Teams.

The affected agent previously worked in Teams for several weeks before the issue appeared.

The agent architecture is very simple (single MCP server, no custom connectors, no Power Automate involved in this scenario).

At this point, I'm mainly trying to understand why Teams no longer seems to create a conversation/session for this specific agent while the same agent continues to work in Copilot Studio and Microsoft 365 Copilot.

Has anyone seen similar behavior or found a way to diagnose why Teams is no longer forwarding requests to a specific agent ?

Thank you for help