You will always see the bars on that graph rise prior to delivery months. They are simply dumping more SLV into the market prior to delivery months to SMASH the price of silver down.
Down to 53,604 contracts left to deal with for July
Another 3,167 moved to Sept giving Sept a total of 82,175 for the time being.
Dec up to 9,745 already. December is the largest physical delivery month of the year. Then there are no deliveries until March. So that is the time that they let the price of silver rise some.