Official words from Dairy Queen has not been documented, however, there's an anecdotal report saying that the company changed the name to "Arctic Rush" because someone complained Mister was too masculine and offended their sensibilities.
Dairy Queen’s products over the years expanded to include malts and milkshakes in 1949, banana splits in 1951, Dilly Bars in 1955, Mr. Misty slush treats in 1961 (later renamed Misty Slush, then again to Arctic Rush), and a range of hamburgers and other cooked foods under the Brazier banner in 1958 (which are not yet available to the Hawaiian Islands).
Know more about the history of Dairy Queen at www.dairyqueenhawaii.com.
Sometimes a product's name can be damaged by a change in the marketplace. When a product name is not performing well, you can either tough it out, hoping for a change in the marketplace, or take a proactive approach by changing your product’s name.
Here's How to Change a Product Name as a Marketing Strategy, featured on Chron.com.
And here are some famous examples that illustrate the power of a name change, listed at BrighterNaming.com.