It may be possible that someone deleted their post or their user. Can you specify exactly where the blue dot showed up?
Bellow I describe some more information on the current policies (enforced by our discourse settings). They may provide some more context to your situation.
Post deletion policy
(as of 21st Nov 2020)
Users can remove their posts and the effects will be immediate. This is not the default discourse behavior (the default is leaving it up 24 and only after deleted), but the moderators believed there to be legitimate concern of users to have their content immediately purged from the public and also to avoid some user confusion with the deletion not taking immediate effect.
A user can edit their posts up to 24 hours
New users can edit their posts up to 24 hours after publishing. There are exceptions, though for higher trust level users. See this post for more information:
Deletion of profiles
I believe a user can delete their profile immediately but I haven’t explore what are the effects in terms of posts. If they get deleted as well or just removed the username.