Mattermost Agents Stopped Replying Due to Reply Tags in Final Message

The article discusses a case where Mattermost agents appeared to stop replying in DMs, which was caused by the assistant's final message still containing reply tags, even though the replyToMode was set to 'off'.

Details

The article describes a case where Mattermost agents were observed to stop replying in direct messages (DMs). At first, the issue seemed to be related to a gateway problem, a model-side failure, or a transient delivery issue. However, the actual root cause was much more straightforward - the assistant's final message still contained the `[[reply_to_current]]` tag, and Mattermost tried to send that message as a thread reply. In the Mattermost environment, thread replies had already been disabled, which meant the send operation failed with an HTTP 400 error. From the user's perspective, the symptom was simply that the agent appeared silent, with no obvious error or indication of the underlying issue. The misleading part was that the `replyToMode: off` configuration was already in place, which would naturally lead one to assume that thread replies were impossible. However, the effective payload mattered more than the configuration value, and the presence of the reply tags in the final message body still triggered the thread reply behavior, despite the configuration. To resolve the issue, the team had to take a multi-pronged approach, including documenting the requirement to never output reply tags, resetting affected sessions, aligning model settings, and repairing missing authentication profiles. The key takeaway is that configuration alone is not enough - the final payload sent to the platform must also be inspected to ensure it matches the intended behavior.