http://www.pcgamer.com/call-of-duty-wwii-has-been-accidentally-granting-double-xp-since-launch/

This past weekend was double XP time for Call of Duty: WWII, but a number of players noticed, and complained, that they weren't actually getting double XP. It turns out that they were right—not because Sledgehammer forgot to turn it on, but because it forgot to turn it off. 

"We launched with 2XP active, unintentionally. Everyone was getting 2XP since 11/3 [the COD:WWII release date] and up until we made the playlist change late Thursday night, which effectively launched 3XP," Condrey explained in greater detail on Reddit. "Come Monday, when we turn off the XP bonus, it will effectively revert to what we should have had at launch (aka 1XP).  So early players, you got a huge head start."