tell me who knows. what it means: generated but not accepted. for the year that the coin is mined. such 6 times was! and why developers are silent. maybe they threw a coin?
It means that you mined an orphan block. When 2 or more people mine the same block at almost exactly the same time only 1 person is allowed to have it and so when this happens the winner is the one with the least amount of network latency...
This is a phenomenon that is common to cryptocurrency in general.