Usually (most of the time, exceptions seem to be around big multiyear trend reversals) big price drops origin from the mass dump / shrinking of the futures component in the spot price.
The last such dump was a serious one:
09/06/2015 35941 $16.13
02/06/2015 57569 $16.70
Just 57 cents, yet the futures component shrunk with 21628 x 5000 = 108 Moz, being over 10% of an annual traded, in a single week.
Apparently, quite some buying on the cash market offset the effect of it. A "normal" drop would have been $1.5 (so $15.2 instead of $16.13).
This situation barely changed since end last year, in the years before, everytime a new low occurred, this has, at the moment, stalled.