If your rank and stats have become corrupted, the Call of Duty servers will restore them using the most recently stored backup. This means that your rank and stats may not be exactly where they were before the reset occurred.
One of the main contributors to rank and stat resets or rollbacks is data corruption, which can occur for a variety of reasons, including
playing on a shared connection — shared connections can suffer data loss
playing on a Wi-Fi connection — wireless connections tend to be unstable due to NAT restrictions
quitting matches early — leaving a public match early could impact data from previous matches
exiting the game early — leaving the game entirely before a public match is complete could impact data from previous matches
The best way to protect your rank and stats from potential corruption is to always play public matches over a wired connection, never play on a shared connection, and always complete public matches.