You mentioned the board is set to private, so I will assume not even your team can access the board. But if this is not the case, some possible explanations are:

• Someone on your team set the board's Visitor/"Anyone with the link" to "Can edit" and then a non-signed in person accessed the board (could have been the same person that changed the board's Visitor settings).
• Someone on your team renamed their Miro account profile name to "visiting visionary" as a joke.
• Someone has accessed your account profile and changed the board's Share settings.

Thanks, I checked shared settings and cannot find anything unusual - will keep my eyes peeled and comment here if it happens again.

Thanks

Hey @Lee Austin, @Robert Johnson,

Alyona from Miro Support is here for a moment   

One more possible scenario is the board being embedded in another website/app and accessed by users there. Feel free to check this handy article for more details: Sharing boards in embed integrations.

SOLVED:

We used the MIRO app from within Google Meet, this creates temporary profiles for users.

Thanks for the help!