Noted. I'll look into it, however the bottom block also has problems. I'll split this off into two issues, this for the side block and the new one for the bottom one.
Automated response: Users online block does not show Display name
The side_users_online block uses usernames (cached from the sessions table) instead of display names. Ideally, it should use display names. This will have a tiny performance hit as we need to query for the display name. But considering blocks have a cache, this shouldn't be a problem.
The side_users_online block uses usernames (cached from the sessions table) instead of display names. Ideally, it should use display names. This will have a tiny performance hit as we need to query for the display name. But considering blocks have a cache, this shouldn't be a problem.