How to explain empty blocks?

Hi, I'm curious about those empty blocks on etherscan so I did some research, one explanation is like this: after receiving a message of new block from network, miner start use the block hash to build a new block while download block body from network, they can't include any transactions in the new block because they might already included in the previous one.

This makes sense, but it can't explain why there is always a non-empty block after those empty blocks about 1 second later. Any ideas?