SLV's Curious Mid-month Silver Swap

For years, SLV had consistently maintained 103.2M ozt silver in their NYC vault. That changed late last year. For the last 5 months, once per month - around the middle of the month, SLV has drained 3M ozt (~93.3t) from it's NYC vault (in ozt):

Nov20 London3.6M
Nov20 NYC3M
Shares700K, Net Stock600K

Dec16 London1.6M
Dec16 NYC3M
Shares1.5M, Net Stock1.4M

Jan16 London3.3M
Jan16 NYC3M
Shares400K, Net Stock300K

Feb19 London34K
Feb19 NYC3M
Shares3.35M, Net Stock3.034M

Mar16 London4M
Mar16 NYC3M
Shares1.2M, Net Stock1M

In November, January and March, the NYC vault drain was offset completely by a corresponding increase in the London vault. These events look like JPM doing a NYC-London swap. Ie. JPM traded SLV's NYC silver in their COMEX [E]ligible vault to some actor in London (possibly even JPM itself) for silver in London which could be deposited into the SLV London vault/account. These events all occurred on days where SLV increased shares (which require deposits of silver into the SLV vaults).

In December, the NYC vault drain was only partially offset by a corresponding increase in the London vault. This occurred on a day where SLV decreased shares. The London offset was sufficient to make up the difference from what looks to be a planned/scheduled 3M ozt drain of NYC stock.

February stands out as a month where the NYC vault drain had no offset at all in the London vault. SLV posted a large decrease in shares that required a larger than 3M ozt drain.

Observations:
These once monthly NYC 3M ozt drains are not related to/dependent upon/triggered by SLV share redemption/creation needs
These once monthly NYC 3M ozt drains look like they were designed to be swaps for London vault stock, SLV share redemptions allowing
JPM is the custodian for SLV's London and NYC vaults
JPM also manages non-SLV house and customer vaults in NYC and London
JPM could theoretically be managing the swaps entirely in house amongst their own vaults

Speculation​

The big question is, "why?". Why is JPM swapping 3M ozt of SLV's NYC silver for silver in London?

I can think of a few possibilities:

JPM is effecting the swap (possibly with a 3rd party) to relieve demand (and price) pressure within the LBMA system

JPM initiated these monthly NYC drains in the aftermath of LBMA silver market seizing up in October because their liquid free float had essentially bottomed out. Silver supply in London was very tight. Elevated lease rates have continued to signal that, while the LBMA's liquid free float is greater than zero, it's not by much - there is still tightness in London. Swapping 3M ozt of NYC silver for London silver allows JPM to source 3M ozt of silver for SLV in the LBMA vault system without having to buy it. As SLV's London vault is the largest slush fund that provides emergency liquidity to the LBMA silver market, JPM prefers to maintain a larger share of SLV vault stock in London.

JPM is managing the swap amongst its own vaults in order to free up 3M ozt of silver for their COMEX [E]ligible stock

When the first swap was effected on November 20, JPM COMEX vaults held:

[R]egistered = 30.3M ozt
[E]ligible = 169.3M - 103.2M SLV = 66.1M ozt

JPM's [E] stock (less SLV) was roughly 1/3 of the total COMEX [E] stock. They had (and still have) plenty of [E] stock. It seems unlikely that JPM is effecting these swaps in order to shore up an already massive [E] stock.

Today (five months later), JPM COMEX vaults hold:

[R]egistered = 12M ozt
[E]ligible = 138.1M - 88.2M SLV = 49.9M ozt

Did JPM foresee the need to drain SLV's NYC vault to support COMEX trading over the last few months? Without the monthly SLV 3M drain, JPM's [E] vault would have 34.9M ozt presently. That's still quite a lot - it would be the 3rd largest in the COMEX system behind Brinks and Asahi instead of currently being second behind Brinks.

JPM is managing the swap amongst its own vaults in order to free up 3M ozt of silver for their COMEX [R]egistered stock

I checked the COMEX silver stock reports for JPM [E]ligible adjustments to [R] from one day prior to two days after each NYC drain event. There were no JPM adjustments from [E] to [R].

JPM is managing the swap (possibly with a 3rd party) in order to free up 3M ozt of NYC silver to ship to London

I checked the COMEX silver stock reports for JPM [E]ligible withdrawals from one day prior to two days after each NYC drain event:

Nov19
Nov20
Nov21648K
Nov24594K

Dec151.3M
Dec162M
Dec17987K
Dec18646K

Jan151.3M
Jan161.3M
Jan202M
Jan211.3M

Feb18
Feb19
Feb20964K
Feb23

Mar13647K
Mar161.3M

As JPM is the whale vault in the COMEX system, their vault regularly moves from 600K to 2M ozt in a day. It's very difficult to determine if the 3M NYC SLV drain contributed to any additional withdrawals (presumably for shipment to London). It seems to me this reason is plausible but unprovable.