Did you read hosseinimr93's explanation above? It's not a visual bug; they have a limitation as explained by hosseinimr93. They don't want to fill the whole block with a very low fee while they can get far better fee from the block mined.
I know what I am talking about because the very next hour even before viaBTC mined any block, the 19 free transactions that were even no existent disappeared 
I kept following and refreshing the page every few minutes at that time when this happened
Of course, I read every explanation before adding in mine.