Could be ice testing Tim.
Back in 2008 I visited Agusta’s icing trials for the A139 in Muskegon, Michigan — their engineers even travelled from Italy for the program.
They used a Chinook spraying water up front, though I'm pretty sure a Chinook would be too slow for an A321 to follow.
The leeward side of Lake Huron can offer similar icing conditions, and the shoreline loops fit repeated test-run profiles.
Or maybe it’s related to the recent software update that grounded parts of the fleet — hard to say, but something is clearly being evaluated.