Last Rare in map not appearing on minimap

Killed all rare monsters in the map that appear on the minimap there was no icon for the last rare monster to complete the map. Last monster was in a "Ogham's Legacy Large Strongbox" so it didn't show up on the map. Had to search manually. Was about to leave area and just go a different way because I thought that the map completion was just bugged.
Bug Report ID: #3516486085