As a side note of no consequence, during my attempt to find this transition I ran across a block for which I could not determine whether Blockchain was recording or not,
https://www.blockchain.com/btc/block/660500. The block consists only of a coinbase. :/
There's actually more of that empty block, specially on the older days.
The old ones were simply because there are no transaction in the miner's mempool, so they mined the block empty.
The latest are being speculated that those were blocks that're mined split-seconds after the previous block, like your example: block height 660499 has the same timestamp as that empty block.
You might enjoy this discussion:
Bitcoin's Empty Blocks Analaysis.