Persistent 20-file upload limit in Microsoft Teams after reinstalling published Copilot Studio agent and starting a new conversation

Question

Persistent 20-file upload limit in Microsoft Teams after reinstalling published Copilot Studio agent and starting a new conversation

Zhao, Xiaoqiang 0

Hi,

My published Copilot Studio agent in Microsoft Teams is rejecting the first file uploaded to a newly started conversation with the error: "I couldn't accept one of your attachments because this conversation has reached its 20-file upload limit."

Troubleshooting already performed:

Removed the previous conversation history.
Started a new conversation.
Uninstalled the agent from Microsoft Teams.
Reinstalled the published agent in Microsoft Teams.
Uploaded a new file as the first attachment.
Tested different supported file formats, including .vtt and .docx.

The problem persists and the first attachment is rejected as if the conversation already contained 20 files.

Please confirm where the 20-file attachment counter is scoped for a published Copilot Studio/GitHub Copilot harness agent in Microsoft Teams, and how the attachment state can be reset.

thank you.

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Answer 1

Sayali-MSFT 6,501 Microsoft External Staff Moderator

Hello Zhao, Xiaoqiang ,
The 20-file limit appears to be tied to the server-side conversation/session state rather than the local Teams app installation. Therefore, deleting the visible chat history or reinstalling the agent may not reset the attachment counter if Teams continues using the same backend conversation ID.

Since the very first file in a newly started conversation is being rejected, this does not appear to be expected behavior and may indicate stale or incorrectly associated attachment state. Please test once in Teams web/InPrivate and with another user to rule out client caching.

Ujwal C R 0 Reputation points

2026-10-28T16:34:20.5033333+00:00

Hi Sayali,
If it works correctly in Teams Web but the issue persists in the Teams desktop app, could you please advise on the next troubleshooting step?
Sayali-MSFT 6,501 Reputation points Microsoft External Staff Moderator

2026-11-04T09:46:56.4133333+00:00

Hello Ujwal C R,
Thanks for confirming.

Since the upload works correctly in Teams Web but fails in the Teams desktop app, this points to a client-specific issue rather than the Copilot Studio agent or backend conversation state.

As the next step, please completely quit Teams and reset the Teams desktop app from Windows Settings > Apps > Installed apps > Microsoft Teams > Advanced options > Reset, then restart Teams and test again.

If the issue still persists after the reset, please share the Teams desktop version, timestamp of the failed upload, and relevant diagnostic logs/correlation ID so the issue can be investigated further.