According to Odaily Planet Daily, mempool data showed that miners dug out a half-empty block at Bitcoin height 855363, which was only 75 seconds away from the previous block height.

@mononautical, the founder of mempool, said that all the transactions in this half-empty block were broadcasted in the last minute or so. This block may have been mined by a brand new node and accidentally put into production without syncing the memory pool.