Take a look at the recently mined blocks. there are some miners that very frequently mine two blocks within quick succession, like just now for example: Block 930256: https://www.blockchain.com/explorer/blocks/btc/930256 Followed by block 930257: https://www.blockchain.com/explorer/blocks/btc/930257 The second block is usually almost empty.

This can have another explanation as well: the moment a block is found, the miner starts building on top of the previous block but hasn't constructed a new full block of transactions yet as that costs a bit of time to calculate and distribute. In this period, a new block could be found.