If liquidity of ADRs on the NYSE is low and the ADR price runs at a premium to the SSN underlying share price based on liquidity in the AU market, which could also be impacted by currency exchanges rates, then the US depository will see an opportunity to make a few bucks. They will therefore instruct the AU nominee to purchase the stock on the AU market so that the depository can issue more ADRs which it can then sell into the US market.
I believe the nominee is paid to facilitate the AU end of the transaction and hold the stock on behalf of the depository and eliminating the need for the depository to be a member of the ASX and licensed to operate in this market.
While I'm not privy to how the nominee conducts their back office operations I'dd suggest that they use a trading account to slowly acquire the required stock throughout the trading day. This may require many smaller transactions. Once they have the full order they sweep it over the the nominee account for the US depository in a single XT transaction which is what you see.
SSN Price at posting:
12.5¢ Sentiment: Buy Disclosure: Held
