Sorry if this is explained somewhere else, but I saw the latest block was only like 90kb while most others hover around 990kb (and have ~1.5 btc more in transaction fees).
Why are some blocks like this?
Because when Kano takes his 0.9% (making for 1 transaction), it's not an empty block.

Sorry, but I don't understand what you said. I had the same question when I saw the "Block Reward" for the latest block was 12.6 something. Since finding a block is 12.5 BTC right now (I think) does it mean that there were no transaction fees in this block? Sorry if this is obvious to others, but I'm only a month into being a miner. Still trying to figure out how it all works.
Our block came only 6 seconds after the previous block. There likely weren't very many transactions out there to put into our block.