Where did the eighth Buranki fall?
The news reports at around 1:00 into episode 3 state that there are reports of Buranki having fallen in Ohta, Toshima, Chiyoda, Shinjuku, and Sumida wards. We also see footage of a destroyed Buranki in Bunkyo ward. 

Below, I've superimposed a diagram of the wards of Tokyo over the screenshot in the question (which is thankfully fairly easy to do because of the distinctive shape of Tokyo Bay). 



In green, I've outlined Sumida. A Buranki is supposed to have fallen there, but there's no smoke plume. The other wards listed all have smoke plumes in theme, so my best guess is that someone just forgot to draw a plume in Sumida.