Probably a mismatch between buy and sell orders. This could arise because price on Australian market was up sharply overnight so some buyers putting in a low price and sellers putting in a high price based on close in Oz.

I don't know how the mechanism of reconciling the orders is carried out, by NYSE or brokerage firms. It is a bad time to put in a market order as might mean buying at a high price or selling lower than expected; an unpleasant surprise.

WBK is near its recent highs, might be a good time to put in a sell order for part of your holding. It is still a good business by all reports but anything is possible.

LOL