M365 Copilot Agent fails to process runtime Word attachments

We are experiencing a repeatable issue with Microsoft 365 Copilot agents processing Word documents uploaded during a chat.

Steps to reproduce:

1. Start a new chat with an M365 agent.
2. Upload a DOCX file at runtime.
3. Ask the agent to read or analyze the document.
4. The agent fails with: “Sorry, I wasn't able to respond to that. Is there something else I can help with?”
5. The resulting chat is sometimes incorrectly named <br aria-hidden="true">.

The same DOCX processes successfully in standard Microsoft 365 Copilot Chat, isolating the issue to runtime attachment handling within the M365 agent.

This has occurred multiple times with M365 agents. Please investigate whether this is a known issue with runtime file attachments and advise on remediation.