Boss Rush public, the same Sun Giant

I set a portal at my home to a Boss Rush, making the realm public with the tick box hoping to play with others. No matter how many resets or what difficulty the portal is set to, I am brought to the same Sun Giant who can take several thousand damage hits without losing much of his bar at all. This is in direct opposition to other private boss rushes opened at the same difficulty (even encountering sun giants in them).

It seems like setting the boss rush to "public" goes to the same realm where someone may have left at a very high difficulty fight. This persists through portal resets.