Mattermost @mention Expands to Wrong Users Instead of User Group Members

Issue Summary

A newly created User group (e.g., @billing) in Mattermost unexpectedly expanded into a fixed list of usernames instead of referencing its current members. This expansion occurred consistently across all platforms (web, desktop, mobile) and affected all users.

Observed Behavior

When mentioning a user group (e.g., @billing) in a Mattermost message, the system automatically expands the mention into a list of specific usernames, rather than keeping it as a group reference or showing the correct current members.

Other user groups behaved normally, staying as @groupname when mentioned.

Investigation & Root Cause

The issue was traced to a configuration in the Autolink plugin for Mattermost. A regex pattern in the config.json was set to match @billing and replace it with a fixed template of users. This override was applied before the User Group functionality could resolve the mention.


The Autolink behavior is defined in the config.json file ,just open it, search for the "mattermost-autolink" section. 

Resolution Steps

To resolve the issue, open the config.json file, locate the "mattermost-autolink" section, and either remove the matching regex entry or disable the plugin if it's no longer needed.