It looks like JP Morgan is moving its silver from iShares Silver Trust (SLV) to its COMEX warehouse. Look at this table:

data in millions ounces of silver

source: Simple Digressions
 

Note that since 2017 the changes in SLV holdings match the changes in JP Morgan holdings. This pattern is particularly clear this year - JPM increased its holdings by 7.9 million ounces of silver up-to-date while SLV reported a decrease of 7.7 million.

Last year JP Morgan added 37.3 million ounces to its COMEX warehouse while SLV reported a decrease of 20.7 milion.

Now the question is what it is all about. 

By the way, there are 127.3 million ounces of silver at JP Morgan's COMEX warehouse. (as of February 5, 2018). To give you some comparison - the annual silver production is 886 million ounces (2016) so JP Morgan (or its clients) hold around 14.3% of the world's silver production.