After a Discourse forum update, many usernames suddenly had a 1 appended to the end. JamesNorth initially couldn’t find a solution, but later discovered that the issue was due to a change where group names can no longer be the same as usernames, affecting uniqueness. JamesNorth fixed the issue by renaming groups, but found it disappointing to have to go through every user. sam explained that this change was necessary to protect the single namespace, ensuring that @mentioning groups works properly.
Evidently groups can no longer have the same name as users.
So the group name and username now count towards ‘uniqueness’.
Disappointing to have to go through and fix it all (every user has their own group for this business forum), but hopefully this helps someone else with the same issue.