What is the "Count" column in the order book on Bitfinex?
It's because the Total column is not the cumulate sum of the column Count but of the column Amount. In your example, at the line for price 1612, Total=6.0 and indeed if you do the sum of all amount of the price above 1612 it gives you : 0.3+1.2+1.7+2.8 = 6