Bitmain’s mining pool Antpool mined a block at height 584,802 which failed to be appended to the blockchain after full nodes identified the block as invalid. The block was determined invalid due to the block subsidy being 13.26 bitcoin which is more than the 12.5 bitcoin set by the protocol. The event is believed to be due to a software error. Subsequently, Antpool mined a valid block at height 584,802.
Source: Twitter