Copilot Studio Bot Errors: ConversationStateTooLarge and ActionNotFound – Bot stops responding

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Posted on by CU13011012-0

Hi Community,

We are facing an issue with our Copilot Studio bot where the conversation suddenly fails and the bot becomes unresponsive. We are seeing the following errors in the chat:

Sorry, something unexpected happened. We’re looking into it. Error code: ConversationStateTooLarge. Conversation ID: 15d0956a-d258-4fb9-8901-de0d9182cd0d. Time (UTC): 1/6/2026 4:42:37 PM.
Sorry, the bot can't talk for a while. It's something the bot's owner needs to address. Error code: ActionNotFound. Conversation ID: ecc5cdaf-0aa2-47d1-8904-6f87cc9eec69. Time (UTC): 1/6/2026 9:11:00 AM.

Because of this, the bot stops responding for users.

We have explored the error code logs (available here Understand error codes - Microsoft Copilot Studio | Microsoft Learn) and have been unable to find the ConversationStateTooLarge, ActionNotFound error message.

Questions:

What causes ConversationStateTooLarge in Copilot Studio?
How can we prevent conversation state from becoming too large?
What does ActionNotFound mean exactly (missing Power Automate flow/action, deleted action, unpublished changes, etc.)?
What steps should we follow to troubleshoot and permanently fix this issue?

Is there any documentation that explains this error code, and what causes it? I have read through a few forum posts, but wondered if there is any official documentation on the limit we are hitting here.

Any guidance or best practices would be really helpful.

Thanks in advance!

Categories:

Building Copilot Studio chatbots in Microsoft Teams

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S-Venkadesh 1,208 Super User 2026 Season 1 on at

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Hi @CU13011012-0,

if you’re using GPT-4.1, try switching to GPT-5, as it supports a higher token size.

✔️ If this answered your question, please click “Does this answer your question?” so it can help others in the community too.
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Best regards,

S. Venkadesh

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MauroBalsano 6 on at

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Hello @CU13011012-0,

so, ConversationStateTooLarge, seems to occur when too much data is accumulated in the conversation state large variables, full Power Automate outputs, repeated JSON payloads, or looping topics. Once an internal runtime limit is exceeded, the conversation may break and become unrecoverable, while ActionNotFound, often appears afterward, when the runtime can no longer resolve an action due to a corrupted state or unpublished-changed flows.

Regarding the suggestion to switch models, honestly I think that moving to a model with a higher token limit may help in some scenarios, but this issue doesn't seem to be strictly tied to the LLM token window. It appears more related to how much data is stored in the bot's conversation state, regardless of the model used.

In my opinion, reducing state size, avoiding large in-memory objects, republishing the bot and flows, and in last starting new conversations usually resolves the issue.

Let me know if this solves your problem: if so, please mark it as accepted

Regards,
Mauro

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