Scan time 60, expiry 120, and queue 0.  Let it ride, don't fiddle, be patient. 

Simple.  It's got a nice value to the coin.  When it gets low enough that it tops the chart on sites like coinwarz or the like, it suddenly sees an influx of miners flipping to it as the "most profitable coin of the moment".  Difficulty up.  But suddenly, with the huge influx of hashing power, the difficulty shoots up.  Now it's less profitable.  So all the people who just switched to it flip to the next "most profitable coin of the moment".  Difficulty down again.  And so the cycle continues.  I think it's common for big hashers and the multipools.  You can watch this one go up and down all day long.