Hi, Epic changed the way the sens formula works. Everybody's sensitivity value in options got lowered while retaining the same cm/360 (I was at 1.8 sensitivity and now it's set to 1.441... feels like the cm/360 is unchanged but I haven't measured yet). Also you can't set sens lower than 1.0 in the menu anymore.
https://wiki.unrealengine.com/Version_Notes_2017_03_28