A lot of Call of Duty: WWII players are complaining about their getting RANK RESET. The bad news is that there is no way available right to restore your RANK, but the good news is that the exact cause of the issue has been discovered – and if you have started the game all over again to improve your RANK right from the scratch then make sure that you don’t repeat EXACT CAUSE that has been mentioned below.
In order to avoid getting your RANK RESET in Call of Duty WWII, you will have to AVOID PRIVATE MATCHES. As per the details received from a lot of players facing this issue – PRIVATE MATCHES is most likely the main cause of the issue as most of them have stated that they’ve played a private match.
A thread has just come up on WWII sub-Reddit detailing this situation and going by the number of upvotes it has received in just first 5 hours (1644 – 91%). So things are pretty clear as far as I am concerned if you don’t want your RANK to get RESET in Call of Duty WWII then you have to stay away from Private Matches until Sledgehammer Games or Activision introduces a fix for it.
Till then what you can do is try the Singleplayer Campaign of Call of Duty: WWII. You can read or Call of Duty WWII Wiki page. It carries all Walkthrough of all singleplayer missions and many other things.