Cannot access my own board

​@Samuel Turner 

Despite the board having access permissions for ‘everyone’, upon leaving the class I no longer have access to the board.

By ‘everyone’  I’ll assume you mean Visitors/Public/Anyone with the link access.  And while you haven’t said what “I no longer have a access to the board” mean, i.e., what is happening when try to open the board, e.g., asked for a password?, then we have to assume the visitors access what turned off (or someone deleted the board and/or the team where the board resided.

and am the admin of (the board)

If you cannot access the board, then you are either not the board owner (or are not signed in using the Miro account profile that owns the board).

of and even have the board stored on my own google drive. 

If you are referring to the Export → Save to Google Drive feature, this simply makes a link to a Miro board in your Google Drive — this is not a copy of the board itself.

This feels like a bug and I would greatly appreciate some help/support.

If you are not a member of the team where the board resides, then you are cannot be the owner of the board. If this is your situation, then everything appears to be functioning as designed. Your best bet now it to contact the team admin of the team where the board resides to request a copy of the board.